\~  1 1  (*  I /  (* 


I  .  s.  Dl  I'  \K  T.MIA  I    OF    ACKin   I    I  URE 
BUREAU  01  KM'i'M-'I.im.Y     BULLETIN  No.  76. 

L.0  HOWARD,  Eoiomolo«btand<  hMd  Bums. 


FUMIGATION   h\)R  THE  CITRUS 
WHITE  FLY, 

AS  ADAPTED  TO  FLORIDA  CONDITIONS. 


BY 


A.  W.  MORRILL,  Ph.  D. 

SpecieU  Field  Agent. 


WASHINGTON: 

GOVERNMENT     PRINTING     OFFICE 

1*908. 


U.  s.  I  >l  PAR  nil  A  I    (  H     M  rRICl  "I.  I  i  'UK, 
BUREAU  OF  ENTOMOLOGY     BULLETIN  No. 

I      i)    MOW    \KD.  I  „i.>,„..|.....-i  ..n.l  (  l.i.-l  -I  Iturrau. 


FUMIGATION   FOR  THE  CITRUS 
WHITE  FLY, 

AS  ADAPTED  TO  FLORIDA  CONDITIONS. 


A.  \Y.  MORRILL,  Ph.  D. 

Special  Field  Agent. 


[ssi  ed  0<  roBi  i;  31,  L908. 


WASHINGTON: 

GOVERNMENT    PRINTING    OFFICE 

1908. 


.    BUREAU  OF  ENTOMOLOGY. 

L.  0.  Howard,  Entomologist  and  Cktef  of  Bureau. 

C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  absence  of  Chief. 
R.  S.  Clifton,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  special  insect  investigations. 

A.  D,  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  plant  insect  investigations. 

A.  L.  Quaixtance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  apiculture. 

D.  M.  Rogers,  in  charge  of  gipsy  moth  and  brown-tail  moth  work. 

W.  F.  Fiske,  in  charge  of  gipsy  moth  laboratory. 

W.  A.  Hooker,  engaged  in  cattle  tick  life  history  investigations- 

A.  C.  Morgan,  engaged  in  tobacco  insect  investigations. 

R.  S.  Woglum,  engaged  in  hydrocyanic  acid  gas  investigations. 

R.  P.  Currie,  assistant  in  charge  of  editorial  work. 

Mabel  Colcord,  librarian. 

White  Fly  Investigations. 

C.  L.  Marlatt,  in  charge. 

A.  W.  Morrill.  E.  A.  Back.  W.  W.  Yothers.  special  field  agents. 

2 


II  IKK  OF  TRANSMITTAL 


r.  s.  Department  of  A.gri<  [jlture, 

Bureau  of  Entomology, 
Washington,  D.  C.}  Jum  l  /.  t9i 

Sir:  I  transmit  herewith,  for  publication  as  Bulletin  No.  76  of  this 
Bureau,;!  report  on  fumigation  for  the  white  fly,  as  adapted  to  Florida 
conditions,  by  Dr.  A.W.  Morrill,  special  field  agent. 

The  investigation  of 'the  white  fly  problem  in  Florida  is  now  in  its 
second  year,  and  the  results  gained  of  immediate  practical  importance 
are  those  which  indicate  best  methods  of  control.  Fumigation  with 
hydrocyanic-acid  gas  during  the  short  dormant  period  in  winter,  when 
there  are  no  winged  insects,  seems  to  afford  the  greatest  measure  of 
control  or  possible  extermination.  Gas  fumigation  under  the  horticul- 
tural conditions  obtaining  in  Florida  orange  groves  and  the  peculiari- 
t  tea  of  climate  presents  rather  a  distinct  problem.  This  bulletin  gives 
the  results  of  the  fumigation  experiments  of  two  winters  in  Florida, 
and  demonstrates  the  entire  applicability  of  this  method  of  control  to 
the  white  fly.  This  investigation  has  been  under  the  general  direc- 
tion of  Mr.  C.  L.  Marlatt,  Assistant  Chief  of  this  Bureau,  with  Doctor 
Morrill  in  field  charge.  The  latter  was  aided  during  the  winter  of 
1906-7  by  Mr.  Stephen  Strong,  formerly  horticultural  commissioner 
of  Los  Angeles,  Cal.,  and  an  experienced  fumigator,  and  Mr.  .V.  C. 
Morgan,  and  during  the  winter  of  1907-8  by  Messrs.  E.  A.  Back, 
W.  W.  Yothers,  and  R.  S.  Woglum. 

The  wliite  fly  is  the  big  insect  problem  of  Florida  and  other  citrus 
districts  on  the  Gulf  coast,  and  the  information  given  in  this  bulletin 
will  be  of  immediate  practical  value  to  all  citrus  growers  of  the  region 
indicated. 

Respectfully,  L.  O.  Howard, 

Entomologist  and  Chief  of  Bureau. 

Hon.  James  Wilson, 

Secretary  of  Agriculture. 

3 


CON  I  ENTS. 


[ntroducl  ion 7 

Conditions  \.\\  oring  or  necessary  to  good  results    9 

[eolation  of  grove     9 

Court  tic.  I  action 9 

Absence  or  eliminat  ion  of  food  plants  other  than  citrus 9 

ason  of  the  year LO 

Meteorological  elements 11 

i'  i  reee  and  regularit  y  of  Bel  i  ing I  ! 

Equipment M 

Tents 14 

Poles  and  uprights 20 

Miscellaneous  requirements 22 

Chemicals • 25 

Degree  of  purity  required i':> 

Handling,  and  necessil  y  for  protecl  ion  from  moist  ure 25 

Proportion  of  water  and  acid 25 

Procedure 27 

Methods  of  handling  tents 27 

Measuring  i  reee 30 

Method  of  generating  the  gas 35 

Work  routine 36 

Estimation  of  lime  required  for  fumigation  of  grove 38 

Methods  of  computing  approximate  dimensions  and  cubic  contents 39 

Dosage  requirements  for  the  white  fly 40 

Experiment  s  wit  h  sheet  tent 40 

Experiments  with  bell  or  hoop  tent 49 

Miscellaneous  experiments  and  observations 50 

Appearance  of  larvae  and  pupse  of  the  white  fly  when  destroyed  by  fumiga- 
tion   50 

Density  of  the  gas  at  various  heights  above  the  ground 51 

Effect  of  fumigation  on  the  trees 51 

Suggestions  for  the  fumigation  of  small  tree.- 54 

In  the  grove 54 

In  the  nursery 54 

Nursery  stock  for  shipment 54 

Precaut  ions 55 

Expense  of  fumigation 56 

For  equipment 56 

For  chemicals 58 

For  labor 58 

Economy  of  treatment  by  fumigal  ion 59 

I  •  esea  prevented 59 

Cos!  oi  fumigation  compared  with  spraying 62 

Fumigation  versus  natural  control 63 

Appendix 66 

Table  of  dosage  for  the  citrus  white  fly 66 

Index 69 


ILLUSTRATIONS. 


PLATES. 

Page. 

Plate  I.  Figs.  1-3. — Method  of  covering  small  tree  with  bell  or  hoop  tent 1  } 

II.  Figs.  1-3. — Method  of  covering  small  tree  with  sheet  tent  by  means  of 

poles 20 

III.  Figs.  1-5. — Successive  stages  in  the  operation  of  shifting  a  sheet  tern 

from  one  tree  to  the  next  in  the  row.  Fig.  6. — First  tent  ready  for 
introduction  of  chemicals;  "tent  men"  shifting  the  second  tent 
in  the  series 20 

IV.  Fig.  1. — Commissary  tray:  Open  compartment  (tin  lined)  for  cyanid 

at  right,  balances  and  torch  in  the  middle,  compartment  for  acid 
pitchers  and  glass  graduate  at  left.  Fig.  2. — Top  of  derrick,  show- 
ing method  of  attaching  pulley  and  guy  rope.     Fig.  3. — Base  of 

derrick,  showing  method  of  constructing  braces 22 

V.  Fig.  1. — Raising  33-foot  derricks  to  an  upright  position.    Fig.  2. — Der- 
ricks in  position  (one  on  each  side  of  tree),  supported  by  guy  ropes: 

pulleys  hooked  to  catch-rings  in  the  tent 28 

VI.  Fig.  1. — Front  edge  of  sheet  tent  raised  to  tops  of  derricks,  ready  to  be 
pulled  over  tree.      Fig.  2. — Sheet  tent  ready  for  introduction  of 

chemicals 28 

VII.  Fig.  1. — Eighty-foot  tent  covering  large  seedling  orange  tree,  showing 
tent  graduated  for  the  purpose  of  enabling  operators,  to  use  dosage 
table  given  in  the  appendix.  Fig.  2. — Carrying  5-gallon  crocks  con- 
taining acid  and  water  under  the  tent,  preparatory  to  introducing 
the  cyanid 32 

TEXT    FIGURES. 

Fig.  1.  Plan  for  construction  of  octagonal  sheet  tent  50  feet  across,  showing  lines 

used  in  constructing  octagon 16 

2.  Method  of  attaching  hooks  to  tent  when  covering  trees  with  aid  of  der- 

ricks          18 

3.  Plan  for  schedule  board,  showing  convenient  arrangement 22 

4.  Diagram  of  regularly  set  grove  in  process  of  fumigation  with  an  outfit  of 

four  tents 23 

5.  Diagram  of  grove  with  alternating  trees;  first  four  rows  in  process  of 

fumigation  with  four  tents:  three  sets  of  trees  fumigated,  the  tents 
being  moved  from  south  to  north 24 

6.  Diagram  showing  method  of  marking  tents  to  aid  in  obtaining  dimen- 

sions of  inclosed  space  when  covering  tree 32 

7.  Tent  marked  to  aid  in  estimating  dosage,  in  position  for  fumigation 33 

8.  White  fly  {Aleyrodcs  citri) :  Stages  and  details 59 

9.  White  fly  (Alcyrodes  citri):  Adult  male  and  female  and  details 59 

10.  Florida  red  scale  (  Chrysomphalus  feus  I :  Stages 61 

11.  Purple  scale  (Lepidosaphes  beckii  I :  Stages 62 

6 


FUMIGATION  KOI!  Till;  CITRUS  WHITE  FLY,  AS  ADAPTED 
To  FLORIDA  CONDITIONS. 


INTRODUCTION. 

The  discovery  of  the  value  of  hydrocyanic-acid  gas  as  an  insecticide 
against  citrus  pests  is  properly  considered  one  of  tin*  mosl  important 
advances  in  economic  entomology!  This  gas  was  first  used  by  Mr.  D. 
W.  Coquillett,  who  in  1886  was  detailed  by  Dr.  C.  V.  Riley,  the  Ento- 
mologist of  the  U.  S.  Department  of  Agriculture,  to  experiment  with 
insecticides  against  the  cottony  cushion  scale  (Icerya  purchasi  Mask.) 
in  California.  The  process  was  afterwards  brought  to  its  present  de- 
gree of  usefulness  through  the  extensive  experiments  of  Mr.  Coquillet  t . 
and  is  now  generally  recognized  in  the  citrus-growing  sections  of 
California  as  the  most  practicable  and  efficient  method  of  controlling 
the  black,  red,  and  purple  scales.  It  is  now  used  in  combating  citrus 
scales  in  South  Africa,  New  South  Wales,  and  elsewhere,  with  results 
so  satisfactory  that  wherever  it  has  once  been  tested  it  has  proved  its 
superiority  over  all  other  methods. 

In  the  eastern  part  of  the  United  States  Prof.  H.  A.  Morgan 
conducted  experiments  with  hydrocyanic  -  acid  gas  against  citrus 
scales  in  southern  Louisiana  during  the  winter  of  1892-93.  Messrs. 
W.  T.  Swingle  and  H.  J.  Webber,  of  the  Department  of  Agriculture, 
were  the  first  to  use  this  treatment  against  the  white  fly  in  Florida, 
conducting  their  experiments  in  February,  1894.  In  the  winter  of 
1900-1901,  Prof.  H.  A.  Gossard,  then  entomologist  at  the  Agricultural 
Experiment  Station  of  Florida,  aided  during  a  portion  of  his  experi- 
ments by  Prof.  C.  W.  Woodworth,  of  the  Agricultural  Experiment 
Station  of  the  University  of  California,  undertook  some  experimental 
fumigation  work  against  the  white  fly.  The  results  were  sufficiently 
satisfactory  to  lead  Professor  Gossard  to  the  conclusion  that  the 
efficiency  of  this  treatment  against  the  white  fly  is  such  that  if  a 
fumigated  grove  were  segregated  from  all  others,  one  fumigation  would 
render  it  so  nearly  clean  that  it  would  need  no  additional  treatment 
for  two  or  three  years.  It  was  predicted  that  a  process  that  has  been 
found  so  valuable  in  other  parts  of  the  world  is  certain  eventually 
to  come  into  favor  in  Florida. 

7 


8  FUMIGATION    FOR    THE    CITRUS    WHITE    FLY. 

During  the  lasl  few  year-  certain  nurserymen  in  Florida  have  made 
use  of  fumigation  against  the  white  fly  with  good  success,  treating, 
for  the  most  part,  small-sized  trees.  Other  parties  have  tested  fumi- 
gation on  trees  of  all  sizes,  but,  for  lack  of  adequate  equipment  or  of 
a  knowledge  of  the  most  economical  methods  of  procedure  and  dosage 
requirements,  have  not  continued. 

In  January  and  February,  1907,  the  writer,  aided  by  Mr.  Stephen 
Strong,  formerly  horticultural  commissioner  of  Los  Angeles  County, 
CaL,  specially  appointed  in  this  Bureau  as  fumigation  expert,  and 
Mr.  A.  C.  Morgan,  special  field  agent,  temporarily  transferred  from  the 
cotton  boll  weevil  investigations,  conducted  careful  experiments  in 
Orange  County,  Fla.,  in  order  that  fumigation  for  the  white  fly  might 
he  placed  upon  a  practical  basis.  Modern  California  methods  as 
adapted  to  all  sizes  of  trees  were  employed  and  the  principal  results 
are  embodied  in  the  present  bulletin. 

In  December,  1907,  and  January,  February,  and  March,  1908, 
fumigation  experiments  were  continued  by  the  Bureau  of  Entomology 
on  a  larger  scale,  testing  the  conclusions  drawn  from  the  work  of  the 
previous  winter  and  extending  the  investigation  to  cover  the  ground 
more  thoroughlv.  In  this  work  the  writer  was  assisted  throughout 
the  season  by  Messrs.  W.  TT.  Yothers  and  E.  A.  Back,  and  during  the 
month  of  January  Mr.  R.  S.  TVoglum  was  also  engaged  in  the  work. 
Altogether  nearly  4,000  trees  have  been  fumigated  in  Florida  in 
this  experimental  work,  under  the  immediate  supervision  of  the 
agents  of  the  Bureau  of  Entomology.  It  is  too  early  to  include  in 
this  bulletin  more  than  the  general  results  of  the  past  winter's  experi- 
mental work,  but  the  text  has  been  made  to  conform  to  these 
results  as  far  as  worked  out. 

There  remain  many  details  concerning  the  fumigation  process  which 
have  demanded  investigation,  and  at  the  present  writing  these  are 
receiving  attention  by  agents  of  this  Bureau  who  are  conducting  an 
exhaustive  study  of  the  matter  in  California.  The  present  bulletin 
aims  to  give  the  results  of  experiments  in  fumigation  for  the  white  fly 
and  such  information  and  recommendations  as  are  of  immediate 
value  to  these  who  may  contemplate  the  adoption  of  fumigation  as 
a  practice,  or  who  may  desire  first  to  secure  a  small  equipment  in  order 
to  become  familiar  with  the  methods  of  procedure.  The  directions 
given  herein  are  believed  to  be  sufficiently  detailed  to  enable  any 
orange  grower  to  conduct  fumigation,  after  a  few  preliminary  tests, 
without  the  assistance  of  experienced  hands.  The  recently  discovered 
occurrence  of  the  white  fly  in  California  increases  the  importance  of 
definite  information  concerning  the  requirements  as  to  dosage. 

A  new  system  for  the  estimation  of  dosage  is  recommended  herein, 
as  it  is  believed  that  the  usual  method  of  judging  concerning  the  dosage 
requirements  for  scale-insects  can  not  give  the  uniformity  of  results 
which  should  be  obtained  in  using  this  remedy  against  the  white  fly. 


CONDITIONS    PAVORABL1     OR     NKCKSSAKV.  J 

CONDITIONS  FAVORING  OR  NECESSARY  TO  GOOD  RESULTS. 
[SOL  \  i TON    hi     (.i:o\  i.. 

[solation  in  an  Infested  grove  is  the  tnosl  favorable  condition  for  the 
successful  control  <>f  the  white  II  \  by  fumigation.  A  di  (tan<  e  of  one- 
half  mile  between  a  given  grove  and  the  nearest  infested  grove  is 
sufficient  to  insure  against  appreciable  interference  with  the  results  of 
the  treatment  through  the  migration  of  adults  between  th< 
In  many  if  not  inmost  cases  300  or  LOO  yards  is  sufficient  isolation  to 
prevent  the  treatment  being  made  unprofitable  through  such  migra- 
tions. It  is  a  common  experience  in  newly  infested  groves  that  the 
section  which  first  becomes  infested  may  be  very  noticeably  blackened 
by  sooty  mold  for  two  or  three  years  before  the  w  hite  fly  mult  iplies  to 
an  injurious  extent  in  near-by  sections  of  the  same  grove  or  in  immedi- 
ately adjoining  groves.  The  experience  mentioned  above  indicates 
that  in  isolated  groves  the  extermination,  or  nearly  complete  extermi- 
nation, which  can  be  obtained  by  carefully  conducted  fumigation,  will 
result  in  a  condition  of  practical  immunity  over  a  period  of  two  or 
more4  years. 

CONCERTED   ACTION. 

Ranking  next  to  isolation  as  a  factor  favoring  success  in  fumigation 
for  the  white  fly,  is  concerted  action  among  the  owners  of  grove-  in 
naturally  isolated  groups,  or  among  all  the  citrus  growers  in  the  various 
counties.  In  California  the  organization  and  support  of  county  hor- 
ticultural commissions  has  solved  the  problems  connected  with  the 
attainment  of  the  concerted  action  necessary  for  the  control  of  various 
citrus  pests  in  that  State.  It  is  predicted  that  the  white  fly  can  never 
become  a  serious  pest  where  such  systematic  campaigns  against  citrus 
insects  have  been  organized.  In  Florida,  Orange  .County  has  already 
made  a  beginning  toward  the  adoption  of  such  measures  against  the 
white  fly,  having  organized  a  horticultural  commission  with  powers 
equivalent  to  those  of  similar  commissions  in  California.0  The 
officials  having  the  matter  in  charge,  however,  have  not  felt  justified 
in  attempting  active  field  work  on  a  large  scale  until  careful  experi- 
ments shall  have  determined  what  course  can  be  followed  with  a 
certainty  of  uniform  results. 

ABSENCE    OR    ELIMINATION    OF    FOOD    PLANTS    OTHER    THAN    CITRUS. 

The  presence  of  food  plants  of  the  white  fly  other  than  citrus  trees, 
in  citrus  fruit  growing  sections,  constitutes  a  serious  menace  and  in 
itself  often    prevents   successful    results  from   remedial  work.     For- 

«  For  the  California  law  see  Bui.  (il,  Bur.  Ent.,  U.  S.  Dept.  Agric.  (190(5).  pp.  13-21. 


10  FUMIGATION    FOR    THE    CITRUS    WHITE   FLY. 

tunately  the  list  of  food  plants a  is  limited,  and  the  greater  number 
of  those  thus  far  recorded  is  subject  to  infestation  only  when  located 
near  or  in  the  midst  of  heavily  infested  citrus  groves.  The  food  plants 
which  are  of  most  importance  in  connection  with  the  white  fly  control 
are  the  chinaberry  trees,  privets,  and  cape  jessamine,  and  these — 
except  for  the  last,  in  certain  sections  where  grown  for  commer- 
cial purposes — can  be  eradicated  readily,  or  their  infestation  may 
be  prevented  where  community  interests  precede  those  of  the  indi- 
vidual in  controlling  public  sentiment.  These  food  plants  favor  the 
rapid  dissemination  of  the  white  fly  from  centers  of  infestation  and 
their  successful  establishment  in  uninfested  localities.  They  seriously 
interfere  with  the  success  of  fumigation,  as  well  as  of  all  other  remedial 
measures,  by  furnishing  a  favored  breeding  place  where  the  white  fly 
can  regain  its  usual  abundance  in  a  much  shorter  time  than  would  be 
the  case  if  it  were  entirely  dependent  upon  citrus  fruit  trees  for  its 
food  supply.  The  plants  mentioned,  together  with  Citrus  trifoli-ata 
(except  where  used  in  nurseries),  and  all  abandoned  and  useless  citrus 
trees  should  be  condemned  as  public  nuisances  and  destroyed  in  all 
communities  where  citrus  fruit  growing  is  an  important  industry. 
Where  the  destruction  of  chinaberry  trees  is  impracticable  for  any 
reason,  they  may  be  rendered  innocuous  by  taking  steps  to  prevent 
their  becoming  heavily  infested  each  year.  This  may  be  accomplished 
by  either  defoliating  each  winter  or  by  destroying  entirely  all  privets 
and  cape  jessamines  and  by  thoroughly  fumigating  each  winter  all 
citrus  trees  within  a  distance  of  200  or  300  yards  of  each  chinaberry 
tree. 

SEASON    OF    THE    YEAR. 

Fumigation  for  the  white  fly  should  be  done  during  December, 
January,  and  February,  beginning  not  earlier  than  sixteen  to  twenty 
days  after  the  adults  have  disappeared,  in  order  that  all  of  the  eggs 

«  The  complete  list  of  food  plants  so  far  as  known  is  as  follows:  Citrus  (all  variel  Lea), 
chinaberry  (Melia  azedarach  and  Melia  azedarach  umbraculiformis) ,  cape  jessamine 
(Gardenia  jasminoides),  wild  persimmon  (Diospyros  virginiana),  Japan  persimmon 
(D.  kaki),  privets  (Ligustrum  spp.),  Viburnum  nudum,  Ficus  altissima,  prickly  ash 
(Xanthoxylum  clava-herculis),  cultivated  pear  (Pyrus  sp.),  cherry  laurel  (Primus 
laurocerasus) ,  Prunus  caroliniana,  lilac  (Syringa  sp.).  Water  oak  (Quercus  nigra)  has 
been  reported  as  a  food  plant  of  the  citrus  white  fly,  but  there  is  no  definite  record  of 
the  insect  reaching  maturity  on  this  plant,  and  the  observations  made  in  connection 
with  the  present  white  fly  investigations  show  that  for  practical  purposes  oaks  may  be 
ignored  as  food  plants  of  this  species.  Professor  Gossard  reports  having  observed 
Larvae  of  the  citrus  white  fly  on  scrub  palmetto  (Sabalmegacarpa).  The  author  once 
observed  larva?  on  the  banana  shrub  (Magnolia  fuscatum)  but  apparently  none  reached 
maturity  on  this  plant.  Dr.  E.  A.  Back  has  observed  two  live  larvafi  of  the  citrus 
white  fly  on  oleander  (Nerium  oleander).  These  plants  (oaks,  scrub  palmetto,  banana 
shrul).  and  oleander)  may  be  ignored  absolutely  as  food  plants  unless  it  is  proved 
beyond  doubt  that  it  is  possible  for  the  citrus  white  fly  to  reach  maturity  on  them. 
The  cultivated  fig  (Ficus),  and  thesweet  bay  (  Magnolia  virginiana  I  have  beenreported 
as  food  plants,  but  with  little  doubt  these  reports  are  erroneous. 


<  -  i\  hi  i  [0N8    I   w  OH  \  I  •  I .  i     OB    N  Bl  B88AR1  .  1  1 

deposited  bj  these  adults  may  have  time  t<>  batch.  It  is  Impraetiea 
ble  to  attempt  to  destroj  theeggstage  by  fumigation,  or  a  a  rule  by 
anj •  (»t  her  direct  means.  The  scale-like  stages,  however,  technically 
known  as  the  larval  and  pupal  stages,  arc  readily  destroyed  when  the 
dosage  is  properly  estimated.  In  Florida  the  month  of  January  is, 
everything  considered,  the  most  favorable  month  U>v  fumigating  for 
the  white  fly.  Ordinarily  it  won  Id  probably  be  undesirable  to  continue 
fumigation  after  the  adults  begin  to  emerge  in  considerable  numbers 
in  the  spring.     'Phis  time  of  emergence,  of  course,  varies  according  to 

the  locality  and  to  weather  conditions,  but   in  general  IS  between  the 

middle  o(  February  and  the  first  of  March.  It  remains  for  further 
experiments  to  show  how  far  fumigation  may  be  practiced  with  profit 
at  other  seasons  of  the  year.  It  is  certain,  however,  that  in  cases  of 
emergency,  such  as  the  checking  of  the  spread  of  the  fly  in  newly 
infested  groves,  fumigation  can  frequently  be  used  to  great  advantage 
even  in  midsummer. 

METEOROLOGICAL    ELEMENTS. 

Light. — Fumigation  is  conducted  in  the  absence  of  bright  sunlight, 
to  avoid  injury  to  the  foliage  which  may  occur  when  this  precaution  is 
not  observed.  With  tents  treated  with  oil  to  make  them  nearly  gas- 
tight,  damage  is  almost  certain  to  result  from  daylight  fumigation. 
With  untreated  tents,  however,  the  writer  has  on  several  occasions 
conducted  fumigation  experiments  with  the  sun  fifteen  minutes  high 
without  appreciable  injury  to  the  foliage.  One  orange  tree  was 
fumigated  forty  minutes,  beginning  at  3  p.  m.,  with  the  sun  shining, 
without  any  shedding  or  burning  of  foliage  resulting  from  the  treat- 
ment. The  tent  was  placed  over  the  tree  twenty-five  minutes  before 
generating  the  gas,  and  at  the  beginning  of  the  forty-minute  period 
the  temperature  was  79.5°  F.,  or  4.5°  higher  than  the  outside  tempera- 
ture. Twenty  and  one-half  ounces  of  potassium  cyanid  were  used, 
and  97.7  per  cent  of  the  white  fly  pupae  were  destroyed.  This  amount 
of  cyanid  was  4  V  ounces  less  than  the  amount  called  for  by  the 
table  given  in  the  Appendix.  At  the  time  of  fumigation,  the  foliage 
on  the  tree  was  very  much  curled  by  drought  and  after  a  few  rains 
became  normal  in  appearance  without  the  shedding  of  a  single  leaf. 
The  leaves,  at  the  time  of  the  treatment,  when  torn  seemed  to  be  as 
dry  as  paper,  although  many  pupae  of  the  white  fly  on  neighboring 
trees  in  a  similar  condition  produced  adults,  as  did  the  nine  speci- 
mens which  were  known  to  survive  on  the  fumigated  tree.  It  is 
probable  that  future  experience  will  show  that  trees  whose  foliage  is 
curled  as  a  result  of  drought  are  not  nearly  so  liable  to  injury  by 
daylight  fumigation  as  are  trees  whose  foliage  is  in  perfect  condition. 

Fumigation  can  safely  begin  with  sundown,  or,  during  the  fumigat- 
ing season  in  Florida,  between  4  and  5  o'clock  p.  m.  On  dark,  cloudy 
days  fumigation  seems  entirely  safe  at  any  time  with  untreated  tents. 


V2 


FUMIGATION    FOR   THE   CITRUS   WHITE   FLY, 


Wind.— The  effect  of  wind  upon  the  results  is  so  marked  that 
fumigation  should  not  be  attempted  with  anything  stronger  than 
a  slight  breeze,  particularly  if  the  tents  have  not  been  rendered 
gas-tight  or  nearly  so  by  the  use  of  a  "filler."  It  has  been  found, 
with  an  untreated  tent,  that  with  a  dosage  sufficient  to  destroy  100 
per  cent  of  white  fly  pupse,  a  brisk  breeze  renders  the  results  so 
uncertain  that  the  effectiveness  may  be  as  low  as  30  per  cent  in 
some  sections  of  the  tree,  while  in  others  the  destruction  of  the 
insect  may  be  complete. 

Atmospheric  humidity  and  dews. — The  presence  of  moisture  in  the 
form  of  dew  does  not  seem  to  have  any  deleterious  effect  upon  the 
foliage,  although  in  California  it  is  generally  considered  necessary  to 
materially  increase  the  dosage  in  such  cases  to  insure  the  effective- 
ness of  the  work  against  scale  insects.  Prof.  H.  A.  Gossard a  con- 
cluded that  "  moisture  did  not  seem  to  interfere  with  the  efficiency 
of  the  work,  unless  the  leaves  were  almost  dripping,  when  it  became 
a  factor  of  much  disturbance,  though  not  as  great  as  we  had  thought 
probable." 

The  experiments  conducted  by  the  writer  and  assistants  during 
January  and  February,  1907,  show  that  moisture  on  the  foliage 
during  the  period  of  exposure  has  no  marked  effect  on  the  foliage 
or  upon  the  efficiency  of  the  gas  against  the  white  fly.  In  the  six 
instances  where  the  leaves  were  wet  with  dew,  examination  showed 
that  100  per  cent  of  the  insects  were  destroyed  in  all  cases  but  one, 
and  in  this  only  a  single  specimen  out  of  102  under  observation, 
before  and  after  fumigation,  survived  the  treatment. 

The  results  of  the  tests  concerning  the  effect  of  atmospheric 
moisture  on  the  efficiency  of  the  fumigation  treatment  are  given  in 
Table  I. 

Table  I. — Effect  of  atmospheric  moisture  on  efficiency  of  fumigation.    , 


Experi- 
ment 
No.  b 


Air 
humidity 


Condition     Condition 
of  tent.        of  leaves. 


Per  cent 

of  insects 

killed. 


Amount 
of  cyanid 

used. 


Amoimt 

of  cyanid 

recom- 
mended in 
tables:  45 
minutes 
exposure. 


30.7 

40.2 

45.12 

45.21 

45.22 

45.25 

45.27 

50.2 

60.2 

60.19 


Per  cent. 
100 

94+ 
100 

87 

87 

96 
100 

97 

64 

90 


Wet.... 

..    Wet 

.    Moist 

Wet.... 
Damp . . 

..    Wet 

Damp -1 

Damp . . 
Wet 

.1  Moist 

..|  Wret 

.    Moist 

Damp . . 
Damp.. 

.    Dry 

.    Dry 

100 

100 

100 
89.  3 
99.8 

100 
99.7 

100 

100 

100 


Ounces. 
30 
32 
15| 

9 

133 

33i 

36J 

28 

22 

27} 


Ounces. 
24 
27 
14 
11 
18 
32 
34 
19 
26£ 
26A 


a  Bul.  67,  Fla.  Agr.  Exp.  Sta.,  pp.  647-648. 

&  The  number  preceding  the  decimal  point  indicates  the  length  of  exposure. 


(  <>.\  in  I  IONS    I    W  OK  Mil  I     "i;     \  I  i   I  SH  \i:\  . 


18 


( )n  several  occasions  it  was  observed  thai  the  tent  Pell  somewhat 
damp  when  being  handled,  although  the  humidit)  recorded  l>\  a 
standard  sling  peychrometer  bad  no1  reached  complete  saturation. 
On  other  occasions,  as  Bhown  l>\  the  above  data,  the  foliage  was 
covered  with  a  dew  like  ;•  fine  mist  when  the  sling  psychrometer 
indicated  as  much  as  6  per  cent  belo^  complete  saturation.  For 
practical  purposes,  bowever,  the  moisture  <>n  the  leaves  may  be 
considered  as  Indicating  ;i  condition  <>f  inn  per  cent  atmospheric 
moisture.  Blank  spaces  in  the  table  indicate  that  no  note  was 
made  concerning  this  particular  point,  although  the  tent  was  evi- 
dently "wet"  in  experiments  10.2  and  50.2  and  the  leaves  were 
evidently  "dry"  in  experiments  45.21  and  45.22.  In  the  experi- 
ments summarized  in  Table  I  the  possibility  of  reducing  the  efficiency 
of  the  gas  through  absorption  by  the  moisture  on  the  leaves  and 
tent  had  to  l>o  taken  into  consideration.  To  eliminate  this  feature 
and  to  determine  the  effect  of  the  pis  on  larvae  and  pupae  of  the 
white  fly  when  leaves  are  wet  artificially,  tests  were  made  by  wetting 
the  leaves  both  by  dipping  and  by  means  of  an  atomizer.  The 
results  are  summarized  in  Table  II. 


Table  11.     Eifa-t  of  artificially  wetting  hairs  on  efficiency  of  fumigation. 


Experi- 
ment 
No. 

Air  hu- 
midity. 

Amount 
of  cyanid 

used. 

Amount 
of  cyanid 
recom- 
mended 

in  table. 

Total 
number 

Of  insects 
under 

observa- 
tion. 

Per  cent 

of  insects 
killed. 

Number 

of  insects 

on  leaves 

wet  arti- 
ficially. 

Per  cent 
of  insects 
killed  on 
leaves 
wet  arti- 
ficially. 

Method  of 
wetting. 

Per  a  ni. 

Ounces. 

Ounces. 

30.6 

44 

20 

29 

242 

71 

21 

95.  2 

Dipped. 

lni. 

47 

\:\ 

21 

392 

88 

1  )M 

90.6 

Sprayed. 

1(1.7 

.>.. 

s| 

13 

132 

80 

40 

87.5 

Dipped. 

10.8 

61 

i"! 

29j 

223 

96 

93 

98.9 

Sprayed. 

40.9 

54 

12 

27 

342 

93 

20 

95 

Sprayed. 

40.1:5 

63 

-1 

28 

730 

KM) 

567 

100 

Dipped. 

Ill  the  above  experiments — omitting  the  last  one,  in  which  all 
insects  were  killed — 1,331  insects  were  under  observation.     Of  these, 

323  were  on  leaves  wetted  artificially.  The  weighted  average  of  the 
insects  killed  on  these  leaves  is  92.5  per  cent.  Of  the  1,008  insects 
on  the  dry  leaves  852,  or  84  per  cent,  were  killed.  This  seems  t<> 
be  of  considerable  significance  in  view  of  the  fact  that  in  every 
instance  where  less  than  100  per  cent  of  the  insects  were  killed,  the 
percentage  of  killed  was  greater  on  the  artificially  wetted  leaves 
than  on  the  dry  leaves. 

Taken  as  a  whole  the  results  summarized  in  the  two  foregoing 
tables  show  conclusively  that  moisture  on  the  leaves  in  the  form  of 
dew  does  not  reduce  the  efficacy  of  the  gas  in  destroying  the  insects, 
but  possibly  increases  it.  In  the  experiments  in  which  moisture  was 
a  factor  no  injury  to  the  foliage  followed,  even  when  the  dosage  was 
increased  fully  one-half  above  the  amount  called  for  by  the  table 
in  the  appendix  of  tins  bulletin.     The  results  give  no  justification  to 


14  FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 

the  practice  of*  some  funiigators  who,  as  has  been  stated,  increase  the 
dosage  when  the  tents  and  foliage  are  wet  with  dew.  It  seems  that 
the  difficulty  in  handling  wet  tents  is  the  only  consideration  for 
which  it  is  necessary  to  cease  work  on  foggy  nights,  every  thing  else 
being  favorable. 

SIZE    OF   TREES    AND   REGULARITY    OF    SETTING. 

While  it  is  true  that  it  is  possible  to  place  a  fumigating  tent  over 
any  citrus  tree  regardless  of  size,  the  author  strongly  recommends 
that  orange  growers  make  a  practice  of  p;*uning  large  seedling  trees 
so  that  they  will  not  exceed  28  or  30  feet  in  extreme  height.  Such 
pruning  will  greatly  reduce  the  cost  of  labor  in  fumigating  and  will 
be  of  considerable  advantage  from  the  standpoint  of  picking  the 
fruit.  It  is  probable  that  the  now  generally  recognized  all-around 
advantage  of  low-pruned  fruit  trees  applies  equally  well  to  citrus  as 
to  other  kinds  of  fruits.  Another  consideration  of  importance  is 
the  regularity  in  the  setting  of  orange  groves  and  the  proper  spacing 
of  trees.  In  Florida  various  factors  have  resulted  in  many  groves 
being  too  crowded  or  too  irregularly  set  to  permit  of  the  easy  handling 
of  fumigating  tents.  While  it  is  well  to  bear  these  things  in  mind 
to  the  end  that  all  Florida  groves  may  gradually  be  adapted  to 
reduce  the  labor  and  expense  of  fumigation,  yet  even  under  present 
conditions  it  is  exceedingly  rare  that  fumigation  is  rendered  abso- 
lutely impracticable  by  the  size  of  trees  or  the  irregularity  of  their 
setting. 

EQUIPMENT. 
TENTS. 

Styles  of  fumigating  tents.— Two  styles  of  tents  are  now  in  use  for 
orchard  fumigation,  the  bell  or  hoop  tent  (PI.  I.)  and  the  sheet  tent. 
The  first  is  bell-shaped  and  held  open  at  the  mouth  by  a  hoop  of  }-inch 
gas  pipe.  Tents  of  tins  style  are  preferable  for  use  only  when  the 
trees  in  a  grove  are  uniformly  less  than  12  feet  in  extreme  height. 
Sheet  tents  are  made  in  the  form  of  flat  octagons  and,  being  adapt- 
able for  trees  of  all  sizes,  are  in  California  used  almost  exclusively. 
Plate  I,  figure  3,  shows  a  tree  which  is  14  feet  in  extreme  height  and 
14  feet  in  extreme  expanse,  covered  by  a  hoop  or  bell  tent.  When  the 
tent  is  in  position  covering  the  tree  the  measurements  are:  Height, 
13  feet,  and  diameter,  12  feet.  Hoop  tents  are  not  always  easily 
placed  in  position  over  trees  of  this  size,  and  it  is  believed  that  ordi- 
narily a  sheet  tent  is  more  desirable  for  trees  of  all  sizes.  A  third 
style  of  tent  which  will  be  found  useful  in  fumigating  small  trees  is 
the  box  tent  in  the  form  of  a  rectangular  prism.  This  will  probably 
prove  advantageous  for  trees  5  feet  or  less  in  height.  The  light 
wooden  framework  supporting  the  cloth  cover  gives  a  form  to  the 


Bui.  76,  Bureau  oi  Entomol 


Plate  I. 


Figs.  1-3.-Method  of  Covering  Small  Tree  with  Bell  or  Hoop  Tent.    iOriginal.) 


I  5 

inclosed  space  which  permit  of  economical  use  of  chemical  with 
greater  uniformity  of  re  ill! 

natruction  of  tints.     The  construction  of  the  !>.. 
suggested  in  the  for  ph  is  a  simple  matter  and  con 

venient  patterns  will  suggest  themselves  at  once  bo  anj 
of  fumigating  small  trees.     The  framework  should  be  light  but  u.-il 
braced,  and  for  a  covering  either  6J-ounce  drill,  painted  to  render  m 
n>  nearly  gas  tight  as  possible,  or  oilcloth  is  recommended. 

Prof.  C.  W.  Woodworth,  of  the  California  experiment  station, 
gives  ili»v  following  directions  for  cutting  the  cloth  for  bell  tent 

\ll  of  these  tenta  are  made  in  the  same  manner   and  are  the  mod  economical  in 
cloth  of  .hi\  tents  made.     Commonl)  the  tenl  i«  made  bj  the  "cul  and  fit  "  method. 
These  tenta  maj   be  made  \\iili  Bcarcelj  an)  loss,  ii  cut  according  to  t hi-  folli 
directions:  Measure  off  strips  of  a  length  equal  to  twice  the  height  plus  one-tenth  the 
diameter  of  the  tent  desired.    These  w  ill  make  twi  each  by  marking  the  • 

middle  and  measuring  off  on  one  edge  from  tin-  middle  Lint >-quartero4  the  diameter 

of  the  tent  and  on  the  other  one-half  the  diameter.  Now,  take  a  long  strip  of  molding 
and  bend  ii  bo  as  to  touch  these  three  points  and  mark  off  the  curve  bo  produced. 
Tins  allows  for  the  seam.  In  making  up,  sew  the  two  cul  edges  together  in  each  pair 
of  b1  rips. 

ka  has  been  stated,  sheet  tents,  or  more  properly  covers,  are  flat, 
regular  octagons.  The  dimensions  are  sometimes  stated  in  terms  of 
the  true  diameter  (i.  e.,  the  distance  between  opposite  corners  . 
but  for  practical  purposes  the  distance  between  parallel  sides  should 
represent  the  size  of  the  tent,  for  the  reason  thai  this  represents 
within  about  2  feet  (which  must  be  allowed  to  rest  on  the  ground) 
the  distance  over  the  tallest  tree  that  a  given  sheet  can  cover  meas- 
uring from  the  ground  on  one  side  to  the  ground  on  the  other,  over 
the  center  of  the  tree. 

I  [ereafter  in  this  bulletin  the  size  of  octagon  covers  as  stated  should 
be  understood  to  refer  to  the  distance  between  parallel  sides.  The 
specifications  should  be  carefully  worked  out  before  Deginning  the 
construction  of  a  sheet  tent  as  well  as  of  other  styles.  First,  the 
dimensions  of  the  tallest  tree  which  the  tent  is  required  t«»  cover 
should  he  estimated.  This  may  he  accomplished  by  throwing  a  tape 
attached  to  a  reel  over  the  top  of  the  tree  and  measuring  from  ground 
to  ground.  When  covered,  the  weight  of  the  tent  will  reduce  the 
extreme  height  of  the  tree  in  most  cases  by  from  2  to  l  Int. 
according  to  the  weight  of  the  tent  and  form  of  the  tree.  It  will  he 
well  to  allow  at  least  4  feet  of  the  tent  to  rest  on  the  ground  when 
covering  the  largest  tree.  The  desired  size  having  been  determined, 
a  diagram  of  an  octagon  should  be  constructed  on  paper,  as  indicated 
in  figure  1.  Each  side  of  the  octagon  when  constructed  will  he 
equal  approximately  to  two-fifths  of  the  distance  between  the  parallel 

«  Circular  No.  11,  Oal.  Agr.  Exp.  Sta.,  pp.  9-10. 
49918— Bull.  76—08 2 


16 


FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 


:b: 


sides  of  the  octagon.  The  number  of  square  yards  of  cloth  required 
is  about  18  per  cent,  or  between  one-sixth  and  one-fifth  less  than 
for  a  square  the  sides  of  which  are  equal  to  the  distance  between 
parallel  sides  of  the  octagon. 

In  California  8-ounce  army  duck  has  been  used  almost  exclusively^ or 
making  sheet  covers,  while  in  Cape  Colony,  South  Africa,  a  No.  10 
duck  ranking  in  weight  between  12-ounce  and  15-ounce  is  commonly 
used.  The  heavier  weights  are  not  only  more  durable  but  presumably 
confine  the  gas  better.  A  good  grade  of  GJ-ounce  drill,  however,  as 
shown  later  by  the  results  obtained  with  a  bell  tent  of  this  material, 
seems  to  be  fully  equal  to  the  8-ounce  duck  commonly  used  in  Cali- 

fornia.  Until  careful 
experiments  shall 
have  determined  the 
relative  tightness  of 
various  weights  of 
duck  it  is  recom- 
mended that  sheet 
tents  be  constructed 
throughout  of  8- 
ounce  duck  or  of  8- 
ounce  duck  in  combi- 
nation with  a ' '  skirt " 
of  6J-ounce  drill. 
The  author  has  seen 
a  sample  of  8-ounce 
drill  which  is  no  more 
expensive  than  the 
best  brands  of  duck 
of  tins  weight,  but  is 
evidently  far  superior 
as  regards  tightness. 
Anyone  contemplat- 
ing the  ordering  of 
a  fumigating  outfit 
should  procure  as  many  samples  as  possible  of  different  brands  of 
suitable  cloth  and  select  the  closest  woven  brand. 

The  strips  when  cut  should  be  overlapped  three-eighths  or  one-half 
inch  and  double  stitched  and  all  raw  edges  should  be  hemmed.  In 
calculating  the  number  and  length  of  strips  the  overlapping  will 
reduce  the  width  of  the  cloth  from  three-fourths  inch  to  1  inch.  As 
an  illustration  of  the  method  of  calculating  the  length  of  the  strips 
used  in  making  an  octagonal  tent  of  8-ounce  duck,  50  feet  may  be 
taken  as  the  desired  size.  This  is  equal  to  600  inches  and  the  width 
of  the  cloth,  if  29.5  inches,  will  be  reduced  to  28.5  if  overlapped  one- 
half  inch  at  the  seams.     By  dividing  28.5  inches  into  600  inches  the 


10 


13 


Fig.  1.— Plan  for  construction  of  octagonal  sheet  tent  50  feet  across, 
showing  lines  used  in  constructing  octagon:  A,  C,  side sections;  B, 
central  section  of  full-length  strips;  E,  E,  so-called  "  ends  "  of  tent; 
S,  S,  so-called  "sides"  of  tent;  jR,  R,  reinforcements;  1-21,  strips 
of  duck  29|  inches  v.ide,  overlapped  J  an  inch  at  the  seams. 
(Original.) 


J  7 

nearest  multiple  is  round  t«>  be  598.5  inches,  or  19  feet  and  lOj  in< 
which  is  sufficiently  dose  to  I  he  desired  width  for  practical  purj> 
The  number  of  Btripa  in  a  tent  598.5  inches  wide  is  21.  The  middle 
section  11  (fig.  I)  is  approximately  two-fifths  the  entire  width,  or 
239.5  inches.  Deducting  this  from  598.5  inches,  the  entire  width, 
the  remainder,  359,  equals  the  sum  of  the  widths  of  sections  A  and  C. 
These  sections  being  equal,  the  width  of  each  is  I7(.>.">  inches.  The 
number  of  strips  in  each  section  can  now  !>e  readily  calculated.  The 
21  strips  should  be  numbered  on  the  diagram  From  left  to  right. 
Section  A  requires  six  strips  and  8.5  inches  of  the  seventh.  Simi- 
larly, section  C  requires  six  strips,  beginning  at  the  right  (twenty-first 
to  sixteenth,  inclusive),  and  8.5  inches  of  the  fifteenth.  Section  B 
requires  the  remaining  20  inches  of  strip  No.  7,  '20  inches  of  strip 
No.  IT),  and  seven  entire  widths,  thus  making  the  total  of  21  strips 
required. 

The  cutting  of  the  cloth  can  he  done  without  waste  if  the  details 
of  construction  are  well  planned.  In  the  above  lent  seven  strip-  50 
feet  long  (49  feet  LOj  inches)  should  first  he  cut  for  section  B.  Strips 
Nos.  7  and  15  are  next  cut  and  the  outside  corners  cut  at  an  angle 
of  45  degrees,  as  indicated  in  the  diagram.  Each  strip  for  set  'ions 
A  and  C  is  cut  shorter  by  its  own  width  outside  at  each  end  than  the 
strip  preceding  it.  Thus  the  required  lengths  of  the  side  strips  are 
found  by  matching  the  inner  edge  of  the  new  one  to  the  outer  edge 
of  the  one  before  it.  It  is  desirable  to  have  the  central  section,  B, 
made  up  entirely  of  full-length  strips  so  that  the  stress  will  not  be 
across  seams.  The  stress  is  so  slight,  comparatively,  in  the  side 
sections  A  and  C,  that  this  is  not  an  important  point. 

Shrinkage  of  the  goods  after  being  thoroughly  wet  is  an  impor- 
tant  consideration  in  the  economical  construction  of  fumigating 
tents.  In  order  that  the  tents  approximate  a  regular  octagon,  after 
having  been  used  for  fumigating  purposes,  it  is  necessary  either  to 
have  the  goods  thoroughly  shrunk  before  cutting  or  to  make  allow- 
ance for  subsequent  shrinkage  by  cutting  the  strips  longer.  A  test 
made  with  a  brand  of  8-ounce  duck  commonly  used  in  California  for 
fumigating  tents  showed  that  the  shrinkage4  lengthwise  of  the  goods 
amounted  to  7.5  per  cent,  and,  crosswise  0.9  per  cent;  this  means 
that  in  a  50-foot  tent  the  shrinkage  would  result  in  the  full-length 
strips  shortening  3|  feet,  while  the  tent  would  shrink  less  than  6  inches 
crosswise  of  the  strips.  Such  irregularities  might  be  remedied  by  a 
skirt  of  6\-ounce  drill,  but  it  is  simpler  to  plan  to  have  each  strip 
cut  longer  by  a  given  amount  for  each  1  per  cent  of  difference  in  the 
lengthwise  and  crosswise  shrinkage.  In  the  case  referred  to  above 
this  difference  is  6.6  per  cent,  and  each  per  cent  represents  an  actual 
difference  of  6  inches.     A  50-foot  tent  constructed  in  this  manner 


18 


FUMIGATION    FOR    THE    CITRIS    WHITE    FLY. 


would  therefore  measure  before  shrinkage  52J  feet  (V.)  feel  lOj  inches 
+  3  feet  4  inches)  lengthwise  of  the  strips  through  the  middle  section. 
and  49  feet  10J  inches  crosswise  of  the  strips.  After  shrinking,  the 
dimensions  would  be  approximately  49  feet  4J  inches  in  each  direc- 
tion. The  two  sides  of  the  octagon  which  are  formed  by  the  ends  of 
the  full-length  strips  are  known  as  the  "ends"  of  the  tent  and  the 
sides  of  the  octagon  which  are  parallel  with  these  strips  as  the  "sides" 
of  the  tent. 

By  gathering  the  cloth  around  a  tightly-rolled  wad  of  burlap  and 
tying  on  an  iron  ring,  a  convenient  arrangement  is  made  for  attach- 
ing the  hooks  or  poles  when  covering  trees. 
(See  fig.  2.)  In  the  case  of  the  smaller  sizes 
of  sheet  tents,  which  are  to  be  handled  with 
simple  poles,  these  rings  are  unnecessary,  at- 
tachments being  made  in  the  manner  here- 
after described.  For  large  tents,  measuring 
more  than  42  or  45  feet,  it  is  probably  best 
to  use  the  rings  in  all  cases.  It  is  most  con- 
venient to  have  one  of  these  rings  located  a 
few  feet  in  from  each  of  the  four  corners  of 
the  middle  section  of  full-length  strips  (fig.  1 . 
B) .  In  general,  the  distance  in  from  the  mar- 
gin should  be  from  one-twelfth  to  one-tenth 
of  the  distance  between  parallel  sides  of  the 
tent,  and  the  distance  between  the  two  rings 
on  each  side  should  be  from  one-third  to  two- 
fifths  of  the  distance  between  parallel  sides. 
To  the  ring  mentioned  a  chain  link  is  some- 
times attached  (e),  called  a  "jingler,"  the  ob- 
ject being  to  indicate  the  position  of  the  ring 
when  the  operator  shakes  the  tent,  enabling  him  readily  to  locate 
it  at  night. 

In  order  to  provide  for  the  increased  stress  on  the  cloth  at  the  points 
where  these  rings  are  to  be  located,  a  reenforcement  should  be  stitched 
on  near  each  of  the  "ends"  of  the  tent.  The  main  stress  in  handling 
a  tent  is  directly  behind  the  catch  rings  or  places  of  attachment  when 
poles  are  used  without  rings.  There  is  also  considerable  stress  across 
the  tent  directly  between  the  two  rings  or  places  of  attachment. 
Both  of  these  stresses  may  be  provided  for  by  a  reenforcement  con- 
sisting of  one-half  width  of  the  goods  used  in  constructing  the  tent, 
sewed  entirely  across  the  full-length  strips  of  the  middle  section  and 
extending  2  or  3  feet  onto  each  of  the  side  sections.  These  reenforce- 
ments  are  located  in  accordance  with  the  directions  given  in  the 
preceding  paragraph  and  as  shown  in  figure  1  {B,  B). 


Fig.  2.— Method  of  attaching 
hooks  to  tent  when  covering 
trees  with  aid  of  derricks:  a, 
Tent  gathered  around  ball  of 
burlap  or  other  suitable  ob- 
ject; b,  stout  cord  for  attach- 
ing ring;  c,  catch-ring;  rf,hook 
on  pulley  block;  e,  lap  link 
or  •'  jingler."     (Original.) 


CENTS,  19 

V  -kiii  of  6J-ounce  drill  is  of  considerable  advantage  in  redu< 
the  weight,  especially  in  the  case  <»l  the  larger  sizes  <>f  bents.  This 
drill  is  usually  about  28  inches  wide,  and  when  a  skirl  is  to  be  u  ed 
allowance  is  made  for  one  <>r  two  \\  i<lt  hs  in  const  ruct  ing  i  he  diagram 
and  in  figuring  For  the  cutting  of  the  s  ounce  duck.  Sometimes  the 
skirl  is  run  all  around  the  margin,  bul  it  is  preferable  to  have  the  full- 
length  strips  (section  B)  extended  the  entire  length  <>!'  the  tenl  anil 
the  drill  sewed  to  the  three  sides  of  section  A  and  of  section  C.  When 
the  skirt  extends  all  the  way  around,  \\  lien  shifting  the  tent  b\  means 
of  poles  or  uprights,  the  rings  should  always  he  located  on  the  duck 
inside  of  the  skirt .  to  avoid  too  great  Si  re--  upon  t  he  Lighter  material. 

Painting,  oiling,  mildew-proofing j  and  <-<n<  oj  huts.  Various  meth- 
ods have  been  used  to  preserve  and  to  increase  the  tightness  of  fumi- 
gating tents.  Linseed  oil  was  one  of  the  first  materials  tested  for 
increasing  the  tightness  of  the  cloth:'  hut  experience  has  shown  this 
to  be  undesirable  when  used  either  by  itself  or  in  combinations,  on 
account  of  the  deterioration  in  the  strength  of  the  cloth  and  the  lia- 
bility to  burn  or  rot  when  long  left  folded.  Painting  the  cloth  with 
black  paint,  with  an  inferior  grade  of  glue,  called  asize,"  and  with  a 
mucilaginous  juice  of  the  prickly  pear  cactus  (Opuntia  sp.)  are  three 
methods  mentioned  by  Mr.  D.  W.  Coquillett  in  a  report  dated  in 
October,  1890,  as  in  use  in  California.  In  recent  years  these  three 
methods  have  all  been  used  more  or  less,  the  last  the  most  extensively 
of  the  three.  At  present  the  most  usual  practice  of  California  fu mi- 
gators  is  to  use  untreated  tents  or  tents  proofed  against  mildew  by 
dipping  and  boiling  in  a  solution  of  tannin.  This  last  treatment  is  not 
considered  of  any  value  in  rendering  the  tent  tighter  except  by  ordi- 
nary shrinkage,  which  would  be  accomplished  as  well  in  due  course 
after  using  one  or  two  nights,  particularly  in  Florida,  where  heavy 
dews  are  usual.  The  method  of  treatment  with  the  tannin  solution, 
as  reported  by  a  committee  on  fumigation  appointed  by  the  Claremonl 
(California)  Horticultural  Club  and  published  in  various  horticultural 
and  agricultural  papers,  is  as  follows: 

To  prevent  ruination  by  mildew  when  the  tents  are  damp,  they  must  be  dipped. 
This  is  done  in  a  large  tank,  made  either  of  galvanized  or  boiler  iron.  These  should 
be  3  by  10  feet  and  2\  feet  deep.  The  boiler  should  be  rounded.  This  must  he  on 
a  good  arch,  so  as  to  permit  a  tiro  under  it.  The  smoke  pipe  or  chimney  of  the  arch 
must  be  high,  to  secure  a  draft.  A  derrick  made  by  three  poles  above  the  tank,  sup- 
plied with  pulleys  and  a  rope,  makes  dipping  easy  and  permits  raising  of  the  tent  and 
dripping  after  dipping  is  completed.  It  also  aids  in  keeping  the  tent  from  the  bottom 
of  the  tank  and  burning,  which  must  be  avoided.  The  tank  is  tilled  to  near  the  top 
with  water  and  made  very  dark  by  adding  a  half  barrel  of  oak  extract  or  tannin.  This 
i-  well  stirred.  The  tannin  should  not  be  added  until  the  water  is  boiling.  The  tout 
is  lowered  into  the  tank  of  boiling  water  and  extract  and  boiled  for  half  an  hour,     it  is 

"  Report  of  Commissioner  of  Agriculture.  1SS7.  Report  on  the  Gas  Treatment  for 
Scale  [nsects,  by  I).  \Y.  Coquillett,  p.  12<;. 


20  FUMIGATION    FOR   THE   CITRUS   WHITE    FLY. 

now  raised  from  the  water  and  after  dripping  ceases  it  is  spread  out  to  dry.  The  tank 
is  Idled  again  and  the  tannin  is  added  until  the  color  is  a  reddish  brown,  and  then 
another  tent  may  be  dipped. 

In  Florida  fumigating  tents  become  thoroughly  wet  nearly  every 
night  they  are  in  use,  but  even  when  untreated  will  not  deteriorate 
to  any  great  extent  during  two  or  three  months'  use  if  thoroughly 
diied  each  day,  and  more  especially  before  being  finally  rolled  up  for 
storage  during  the  seasons  when  not  in  use.  Tents  are  conveniently 
dried  each  day  by  simply  leaving  them  on  the  last  tree  covered  until 
dried  by  the  sun.  The  edges  of  the  tent  should  be  straightened  out  as 
soon  after  sunrise  as  possible,  and  folds  in  the  tent  should  be  arranged 
from  time  to  time  to  facilitate  drying.  Such  work,  of  course,  should 
not  ordinarily  be  considered  as  part  of  the  work  of  the  fumigating  crew, 
but  can  be  readily  attended  to  by  some  laborer  employed  at  the  grove. 
It  is  considered  by  some  fumigators  that  when  tents  are  treated  with 
oil  it  is  unsafe  to  leave  the  trees  covered  during  bright  sunlight,  but 
untreated  tents  can  be  safely  dried  in  this  manner.  Drying  is  prob- 
ably hastened  by  pulling  the  tents  partly  off  so  as  to  make  an  open 
space  on  one  side  to  give  circulation  of  air.  Frequently  it  is  a  good 
practice  to  pull  a  tent  wholly  or  partially  over  two  trees  in  order  to 
facilitate  drying.  When  tents  are  dry,  to  prevent  wetting  by  rain 
and  subsequent  trouble  in  drying,  they  should  be  rolled  up  as  com- 
pactly as  possible  and  arranged  to  shed  water  as  well  as  practicable, 
or  they  may  be  covered  with  waterproofed  ducking  or  stored  for  the 
time  being  in  a  dry  place. 

Tents  must  be  kept  in  repair  during  the  fumigating  season  and 
examined  frequently  during  the  daytime  for  holes  which  need  patch- 
ing. If  tents  are  always  pulled  lengthwise  of  the  strips  of  the  cloth, 
there  is  little  danger  of  tearing,  except  when  there  is  much  dead  wood 
on  the  trees.  One  of  the  tents  used  by  the  agents  of  the  Bureau  of 
Entomology  during  the  winter  of  1906-1907  was  used  to  cover 
upward  of  100  trees  without  any  injury  of  this  kind. 

POLES    AND    UPRIGHTS. 

Poles  and  uprights  are  used,  as  shown  in  the  illustrations  (Pis.  II, 
III) ,  for  raising  the  front  edge  of  the  fumigating  tents  when  covering 
a  tree  or  pulling  the  tent  from  one  tree  to  the  next  in  the  row.  The 
simple  poles  are  as  a  rule  used  for  tents  not  exceeding  48  feet  in 
diameter,  and  usually  vary  from  12  to  20  feet  in  length,  according  to 
the  height  of  the  trees  to  be  covered.  In  California  straight-grained 
Oregon  pine  2  inches  in  diameter  is  generally  preferred  for  poles  not 
exceeding  18  feet  in  length;  for  poles  longer  than  18  feet  the  diameter 
should  be  2^  inches.  In  the  Gulf  regions  it  is  recommended  that 
seasoned  cypress  poles  be  used,  as  these  are  much  lighter  than  the 
available  pine.     Although  only  a  single  pair  need  be  used  with  an 


Bui    76,  Bureau  of  Entomology,  U.  S.  Oep! 


Plate  II. 


Figs.  1-3— Method  of  Covering  Small  Tree  with  Sheet  Tent  by  Means 
of  Poles.    ^Original.) 


Bureau  of  Entomology,  u   b  Dopl  of  Agriculture 


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POLES    \M»    i  PBIGH  2  I 

outfit  of  as  in;i!i\  b  twenty  five  or  thirty  tents,  extra  poles  should 
always  be  on  hand  as  a  provision  against  breakage.  A  one  half  \xu  h 
ropeof  either  manila  or  cotton,  about  one  and  one-half  times  the  length 
<>l'  i  he  poles, is  attached  m  I  > « > 1 1 1  3  or  I  inches  from  the  top  of  each  one  that 
is  in  use.  The  tops  of  the  poles  are  constructed  in  various  ityh 
catching  the  rings  on  1 1 1« *  tents.  The  end  of  the  pole  may  be  cut  i<» 
allow  ilit>  ring  to  Blip  <>\rr  the  end  for  a  9hort  distance,  for  instance 
I  or  2  inches,  and  to  hold  the  rope  in  position.  Two  hardwood  pegs 
driven  through  auger  holes  about  l'  inches  apart  at  right  angles  to 
one  another  will  serve  this  purpose.  The  most  convenient  form  for 
genera]  hm>  is  the  simple  rounded  top  over  which  the  cloth  of  the  tent 
is  doubled  and  held  in  place  by  a  half  hitch  of  the  rope  (PI.  II,  figs. 
The  lower  end  of  the  pole  should  be  pointed  to  prevent  its 
slipping  on  the  ground  when  the  tent  is  being  lifted. 

For  use  with  sheet  tents  which  are  too  large  for  convenient  handling 
with  the  poles  described,  a  pair  of  uprights  or  derricks  is  needed. 
These  are  somewhat  heavier  poles,  with  braced  crosspieces  at  the  bot- 
tom tc  prevent  them  from  falling sidewise  when  in  an  upright  position, 
and  each  is  provided  with  a  pulley  at  the  top  (see  PI.  IV,  fi^.  2). 
When  not  attached  to  the  ring  in  the  tent  the  swinging  block  is 
hooked  to  a  ring  holt  or  -tout  staple  located  on  the  upright  near  the 
tops  of  the  braces.  The  poles  are  25  fee.  or  more  in  length,  from  3  to  4 
inches  in  diameter  at  the  base  and  tapering  to  from  2  too  inches  in  diam- 
eter at  the  top.  They  may  be  made  of  straight-grained  knotless  pine  or 
oned  cypress.  Wherever  the  latter  can  be  obtained  it  is  preferable 
to  pine  on  account  of  its  lightness.  A-  shown  in  Plate  IV,  figure  .3, 
crosspieces  about  1  by  3  inches  in  section  are  spiked  or  bolted  to  each 
side  across  t  he  bottom,  and  brace  pieces  about  2  by  4  in  section  extend- 
ing from  between  the  ends  of  the  brace  pieces  to  the  main  pole  are 
bolted  in  position.  The  crosspieces  should  be  i*>  feet  in  length  for 
derricks  25  or  26  feet  high  and  increasing  to  about  "'.  or  8  feet  in 
length  for  32  or  33  foot  derricks.  In  the  writer's  experience  derricks 
are  sufficiently  long  that  are  within  2  to  3  feet  of  the  extreme  height 
of  the  trees  to  be  covered,  as  a  consequence  of  the  elasticity  of  the 
citrus  branches  and  the  fact  that  within  this  distance  of  the  extreme 
top  the  branches  are  almost  invariably  slender.  A  guy  rope  one-half 
or  five-eighths  inch  in  diameter  and  about  one  and  one-half  times  the 
length  of  the  upright  is  attached  to  the  top  of  each,  just  above  the 
pulley  block.  It  is  convenient  to  have  these  ropes  easily  removable 
so  that  they  can  be  used  in  tying  the  tent-  into  compact  bales  when 
rolled  up  for  transportation  or  storage.  The  lifting  tackle  consists  of 
a  rope  of  the  same  size  as  the  guy  rope  and  a  little  less  than  three 
times  as  long  as  the  upright.  One  end  of  this  i-  attached  to  the  fixed 
pulley  block  at  the  top  of  the  upright,  parses  through  the  movable 
block,  then  through  the  upper  fixed  block,  and  the  free  end  is  usually 
tied  to  one  of  the  brace  pieces. 


22 


FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 


MISCELLANEOUS    REQUIREMENTS. 

According  to  the  method  of  procedure  hereinafter  described  and  rec- 
ommended for  use  in  fumigating  for  the  white  fly.  when  an  outfit  of 
more  than  four  or  five  tents  is  in  use,  a  cart  or  stone  drag  and  a  horse 
may  be  desirable  for  carrying  the  materials  from  tree  to  tree.  An 
ordinary  hand  push-cart  can  be  recommended  as  convenient  for  use 
in  some  cases.  When  a  horse  or  a  hand  push-cart  is  not  available,  a 
box-like  tray  (PL  IV,  fig.  1)  with  handles  should  be  constructed. 
This  should  be  large  enough  to  contain  a  supply  of  acid  and  cyanid 
for  all  of  the  trees  covered  at  one  time  by  the  set  of  tents  in  use.  One- 
half  of  the  tray  should  be  reserved  for  as  many  3-quart  pitchers  as 

may  be  needed  and  for  the  graduate,  and  the 
other  half  should  be  provided  with  compart- 
ments for  the  bags  of  cyanid,  if  weighing  is 
done  by  day,  or  an  open  box  for  the  loose 
cyanid  if  the  weighing  is  done  as  each  tree 
is  fumigated.  A  torch  should  be  fixed  over 
the  center  of  the  tray,  and  if  the  cyanid  is 
weighed  as  used  there  should  be  a  strip  of 
board  across  the  tray  to  serve  as  a  platform 
for  the  balances.  Balances  are  preferable  to 
spring  scales  for  use  in  weighing  the  cyanid. 
They  should  not  be  larger  than  necessary  for 
weighing  40  ounces  of  cvanid  at  once.  For 
containing  the  acid  temporarily,  stoneware 
churns  of  a  capacity  of  3  or  4  gallons  are 
much  used  in  California,  and  can  be  recom- 
mended for  use  in  Florida.  Frequently  sev- 
eral 3-quart  pitchers  are  more  convenient  than 
the  stoneware  churns.  A  measuring  glass  of 
16  ounces  capacity  is  needed  for  measuring 
the  acid,  and  an  extra  measuring  glass  should 
be  provided  for  use  in  case  of  breakage.  The 
acid  is  dipped  into  the  measuring  glasses  by 
means  of  a  long-handled  enamel-ware  dipper,  or  poured  in  from  a 
pitcher.     For  carrying  water  a  couple  of  large  pails  are  needed. 

The  one  who  measures  the  acid  and  generates  the  gas  should  be 
provided  with  rubber  gloves  of  good  quality  and  long  enough  to 
cover  the  wrists  well,  or  even  the  entire  forearm.  For  generating  the 
gas,  earthernware  jars  from  1§  to  5  gallons  capacity  are  necessary, 
according  to  the  size  of  the  trees  and  dosage  required.  Extra  jars 
should  be  provided  to  obviate  possible  inconvenience  in  case  of  break- 
age. Cylindrical  jars  are  preferable  to  those  winch  narrow  at  the  top, 
as  the  chemicals  are  much  more  likely  to  boil  over  in  the  latter  than  in 
the  former.     The  cvanid,  after  being  weighed,  may  be  put  into  paper 


A 

o                   A 

B 

O                                                                                    0 

c 

o                                                             o 

o                                                            o 

D 

O                                                                                   0 

Fig.  3.— Plan  for  schedule  board, 
showing  convenient  arrange- 
ment: A ,  space  for  resting  lan- 
tern temporarily;  B,  scratch 
pad;  C,  dosage  table;  D,  dia- 
gram of  grov^.     (Original.) 


I 


Plate  IV. 


Fig.  1.— Commissary  Tray:  Open  Compartment  'Tin  Lined1  for  Cyanid  at  Right, 
Balances  and  Torch  in  the  Middle,  Compartment  for  Acid  Pitchers  and 
Glass  Graduate  at  Left.  Fig.  2.— Top  of  Derrick.  Showing  Method  of 
Attaching  Pulley  and  Guy  Rope.  Fig.  3.— Base  of  Derrick,  Showing  Method 
of  Constructing  Braces.    'Original.- 


KLLANKOUH  HI  Ql   M:i  Ml 


28 


or  into  bin  cans,  or  if  ma}  be  emptied  directl)  from  the  scoop 
mto  the  generating  jar,  \  spade  or  shovel  should  be  on  hand  for 
use  whenever  it  is  necessary  to  weight  down  the  ed  i  of  the  tent  l>\ 
a  lew  Bhovelfula  "t"  earth  and  also  for  use  in  burying  the  content 
the  jars.  A.  copy  of  the  table  of  dosage  required  for  the  white  fly  and 
round  in  the  appendix  of  this  bulletin  mould  always  l>"  on  hand.  A 
convenient  arrangement  for  handling  the  diagram  <>!'  tin-  grove  and 
the  dosage  table  when  fumi  is   illustrated   bj    figure  3.     This 

represents  ;i  board  upon  which  the  position  for  Betting  the  lantern 
temporarily,  and  the  positions  for  attaching  diagram  of  the  grove, 
dosage  table,  ami  scratch  pad  arc  indicated.  For  the  board  a  side 
of  an  orange  box  is  \,.|\  satisfactory.  This  should  be  strengthened 
by   two   lath-  nailed   across   the  grain   on   the   rough  side.     On   the 


10 

9 

8 

X 

N 

7 

X 

X 

6 

5. 

5 

X 

X 

M 

/V 

A/ 

4 

X 

28-36 

9 

33-40 

13 

32-39 

R 

3 

37-45 
17 

25-30 
7 

30-37 

37-48 
18 

2 

30-36 

io'i 

40-61 
25 

33-40 
13 

38-54 
20^ 

X 

1 

38-44 
17 

38-50 

19 

37-51 
19 

36-40 

I4'l 

ABCDEF^GHIJKL 

Fio.  4.— Diagram  of  regularly  set  grove  in  process  of  Fumigation  with  an  outfit  of  rour  tents:  X.  X. 

t  reea  missing.    (Original.) 

smooth  side  at  the  bottom  the  diagram  of  a  portion  of  the  grove 
(fig.  5)  should  be  fastened  with  thumb  tack-.  This  diagram  should 
include  as  much  of  the  grove  as  can  be  fumigated  in  any  one  uighl 
and  should  be  dated  and  preserved  after  the  work  for  the  night  has 
been  checked  off  on  the  original  diagram  (figs.  l.  5  of  the  grove  as  a 
whole.  Immediately  above  the  diagram  the  dosage  table  « t i l: .  3,  I 
should  be  located.  If  the  board  is  smooth  it  may  be  painted  white 
and  the  table  copied  thereon  with  pencil.  If  the  table  i-  on  card- 
hoard  it  may  he  fastened  with  thumb  tack-.  A.bove  the  dos 
table  a  scratch  pad  (fig.  :;.  II    should  !><•  fastened  in  the  upper  right- 


24 


FUMIGATION    FOR    THE   CITRUS    WHITE   FLY. 


W.      5 


hand  corner,  while  the  space  (fig.  3,  A)  in  the  upper  left-hand  corner 
is  left  for  the  fumigator  to  set  his  lantern  while  he  is  writing  down  on 
the  diagram  the  dimensions  of  the  tented  tree  and  the  amount  of 
dosage.  It  will  be  found  convenient  to  attach  a  pencil  to  this  board 
with  a  short  string. 

The  diagrams  of  the  grove  are  prepared  as  shown  in  figures  4  and  5, 
representing  a  small  grove  set  in  regular  and  alternate  rows  respec- 
tively.    When  set  with  any  form  of  regularity  the  individual  trees 
may  be  conveniently  referred  to  by  numbering  the  rows  in  one  direc- 
N  tion  and   lettering 

them  in  the  other. 
Thus  the  first  tree  of 
row  No.  1  is  called 
1A,  the  second  IB, 
etc.,  while  in  the 
other  direction  the 
trees  are  referred  to 
as  2A,  3A,  etc.  In 
measuring  the  cir- 
cumference of  the 
trees  or  in  checking 
the  correctness  of 
the  estimates  based 
on  pacing,  a  75  or 
100  foot  tape  at- 
tached to  a  reel  is 
needed.  Water- 
tight barrels  are  re- 
quired for  contain- 
ing the  stock  of  wa- 
ter for  use  during 
the  night. 

When  weighing 
the  cyanid  a  tin 
scoop  is  sometimes  useful,  and  leather  gloves  should  be  provided 
for  the  one  who  does  the  weighing.  When  weighing  of  the  cyanid 
is  to  be  done  during  the  day  five  wooden  boxes,  with  hinged  covers, 
of  a  size  that  will  conveniently  fit  into  the  cart,  or  one  box  with 
six  compartments,  should  be  constructed  for  use  in  holding  paper 
bags  of  cyanid  in  doses  of  1,  2,  5,  10,  and  20  ounces,  respectively. 
Experience  will  show  the  number  and  style  of  lanterns  and  torches 
required.  A  hammer,  hatchet,  and  other  incidentals  can  be  procured 
as  found  necessary. 


X 

X 

42-54 

24 

43-62 
29 

39-47 
20 

40-49 
21 

X 

41-51 
23 

42-50 
23 

47-60 
34 

40-47 

20 

43-48 
24 

32-38 

13 

42-50 
23 

ABCDEFGH 

Fig.  5.— Diagram  of  grove  with  alternating  trees;  first  four  rows  in 
process  of  fumigation  with  four  tents;  three,  sets  of  trees  fumigated, 
the  tents  being  moved  from  south  to  north:  X,  X.  X,  frees  missing. 
(Original.) 


PBOPOB  riON  O]     w  \  i  i  i;    \  \  i>    \«  n>. 

CHEMICALS. 

DEGRE1     01     PUItm     REQ1   [RED. 

The  materials  used  in  generating  hydrocyanic-acid  gas  are  pota  - 
-in  m  cyanid  KCN),  sulphuric  acid  (H,S04),  and  water.  The  <-\  anid 
and  acid  should  be  purchased  of  a  reliable  dealer.  The  cyanid  should 
be  guaranteed  to  be  98  or  99  per  cent,  which  Is  practically  chemically 
pure.  The  acid  should  be  guaranteed  t<>  be  66°a  and,  as  additional 
assurance,  ii  would  be  well  <«>  have  a  sample  tested  by  a  druggist  or 
by  the  fumigator  himself  1>\  using  an  acid  hydrometer.  This  instru- 
ment is  Inexpensive  and  can  be  obtained  through  any  druggist. 
A  firm  <>[•  hard  cyanid  should  be  obtained  rather  than  a  soft  or 
porous  product . 

HANDLING,    AND    NECESSITY    FOB    PROTECTION    FROM    MOISTURE. 

Potassium  cyanid  can  be  purchased  in  boxes  of  200  pounds  each. 
The  cyanid  readily  absorbs  moisture,  and  for  this  reason  after  a  box 

is  opened  it  should  be  kept  constantly  covered  with  burlap  sacks  and 
protected  against  rain  when  necessary.  When  only  a  few  trees  are 
to  be  treated  and  the  box  of  cyanid  is  not  to  be  completely  used, 
within  a  tew  days  at  the  most,  it  is  recommended  that  it  be  stored 
in  large-sized  tin  cans  with  covers  made  practically  air-tight  by  means 
of  cheese  cloth  or  muslin.  The  acid  when  used  in  large  quantities  is 
purchased  in  drums  containing  about  1,500  pounds.  In  smaller  quan- 
tities it  is  sold  in  carboys  containing  a  little  less  than  200  pounds. 
The  carboys  make  convenient  receptacles  for  handling  in  the  groves. 
In  emptying  from  a  drum  into  carboys  a  large  funnel  of  glass  or 
sheet  lead  is  useful.  When  the  carboys  are  boxed  and  not  other- 
w  ise  provided  with  handles,  strips  of  wood  may  be  nailed  along  paral- 
lel sides  projecting  at  each  end,  so  as  to  make  convenient  handles 
for  two  men.  If  carboys  can  not  be  obtained  or  the  quantity  of  acid 
used  does  not  require  temporary  containers  for  such  amounts,  large 
jugs  may  be  used.  In  all  cases  the  containers,  except  when  in  use, 
should  be  stoppered.  For  this  purpose  wooden  plugs,  made  tight 
with  asbestos, such  as  can  be  bought  in  sheets  from  hardware  dealers, 
may  be  used.  When  the  acid  is  to  be  stored  in  carboys  for  more 
than  a  few  days  the  plugs  should  be  made  extra  tight  by  means  of 
plaster  of  Paris.  For  water  required  in  the  generation  of  the  gas 
anything  that  is  reasonably  clean  will  answer  the  requirements. 

PROPORTION'    OF    WATER    AND    ACID. 

The  proportion  of  the  materials  theoret  ically  required  for  a  complete 
chemical  reaction  is  1  part  of  potassium  cyanid,  1  part  of  acid,  and  2 
parts  of  water.     In  practice,  however,  an  excess  of  acid  up  to  one-fourth 

"Sixiy-six  degrees  sulphuric  acid  is  93  per  cent  strength. 


26 


FUMIGATION    FOR    THE    CITRUS    WHITE   FLY. 


more  than  the  actual  requirement  is  ordinarily  used,  while  it  is  gen- 
erally considered  that  the  use  of  three  or  four  times  as  much  water 
as  acid  reduces  the  danger  of  shedding  of  the  leaves  from  excessive 
dosage.  The  experiments  conducted  by  the  writer  relating  to  this 
point  have  thus  far  given  only  negative  results  by  failing  to  show 
any  relation  between  the  proportion  of  the  water  and  acid  and  the 
effect  of  the  gas  upon  the  insects  or  the  foliage.  In  66  of  the  experi- 
ments summarized  hereafter  a  record  was  made  of  the  proportion 
of  the  water  and  acid.  In  nearly  every  case  the  object  was  to 
determine  the  minimum  dosage  required,  and  while  the  record 
included  the  proportions  of  the  water  and  acid  no  effect  of  the  varia- 
tion in  tins  regard  was  looked  for  until  the  results  were  summarized. 
The  chances,  therefore,  were  equal  in  regard  to  the  selection  of  a  dose 
of  the  required  amount  for  greatest  utility  in  the  various  tests.  The 
results  in  connection  with  the  proportion  of  water  and  acid  used 
are  sfiven  in  the  Table  III : 


Table  III. — Results  obtained  with  varying  proportions  of  water  and  arid. 


Parts  of  water  to  one 
part  of  acid. 

Number 
experi- 
ments in 
which  100 
per  cent  of 
white  flies 
were  killed. 

Number 
experi- 
ments in 
which  less 
than  100 
per  cent  of 
white  flies 
were  killed. 

Total. 

2   

1 

9 
10 

0 
11 

0 

2 
•    5 
17 
1 
9 
1 

3 

14 
27 

1 
20 

1 

2§ 

3 

3§ 

4   .. 

5 

Total 

31                    35 

66 

10 
21 

7 
28 

17 
49 

It  will  be  observed  from  the  table  that  the  results  seem  to  favor  the 
smaller  amounts  of  water  in  proportion  to  the  acid  rather  than  the 
larger  amounts.  The  data  are  not  extensive  enough  to  establish  this 
conclusively,  and  it  is  not  improbable  that  the  difference  in  the 
percentage  of  white  flies  killed  has  no  connection  with  the  propor- 
tion of  water  and  acid.  It  is  at  least  evident,  however,  that  there 
is  no  marked  difference  in  favor  of  the  use  of  water  in  a  proportion 
greater  than  necessary  for  the  complete  chemical  reaction.  The 
Association  of  Horticultural  Inspectors  in  1903  adopted  the  formula 
usually  expressed  1-2-4,  meaning  1  part  of  cyanid,  2  of  acid,  and 
4  of  water.  Mr.  Wilmon  Newell's  laboratory  experiments a  lead 
him  to  conclude  that  this  formula  permits  the  volatilization  of  an 
apparently  maximum  amount  of  prussic  (hydrocyanic)  acid. 

«Bwl.  15,  Georgia  Stale  Board  of  Entomology,  pp.  21-24,  1905.. 


METHODS  O]     HANDLING  TENTH.  Z  ( 

The  element  of  beat  due  to  the  mixing  <>f  the  acid  and  water  ii  rec 
ognizcd  as  an  important  factor  in  generating  the  gas.     According  i<» 
c.  p.  Lounsburj  '  verj  nearly  the  maximum  amount  of  heat  isevolved 
when  equal  volumes  of  acid  and  water  are  used,  and  he  advises  against 
the  use  of  more  than  2  volumes  of  water  to  l  of  acid. 

The  point  in  question  is  one  of  those  n<>\\  under  investigation  in 
California  1>\  agents  of  this  Bureau.  Until  conclusions  are  reached 
the  writer  would  recommend  that  the  chemicals  be  used  in  the  propor- 
tionof  l  pari  of  cyanid,  l  part  of  acid,  and  3  parts  of  water,  or  1-1  3. 
'This  formula  is  recommended  for  the  present  on  account  of  results  of 
experiments  reported  herein  and  upon  which  the  table  given  in  the 
appendix  is  based,  being  obtained  with  an  average  of  3  parts  of  water 
to  I  <>(  acid.  Future  experiments  may  justify  the  California  prac- 
tice from  the  standpoint  of  danger  to  the  foliage  from  the  use  of  the 
smaller  amounts  of  water.  In  the  experience  of  the  writer  as  reported 
herein,  the  injury  to  the  foliage  has  been  too  slight  to  show  any  rela- 
tion to  the  proportion  of  the  chemicals. 

PROCEDURE. 
METHODS    OF    HANDLING   TENTS. 

Sheet  U  nls. — Octagonal  sheet  tents,  or  covers,  are  placed  in  position 
over  trees  by  means  of  the  changing  poles  and  derricks  which  have 
been  described.  A  tree  which  measures  in  extreme  height  between 
30  and  35  feet  can  be  covered  and  made  entirely  ready  for  the  genera- 
tion  of  the  gas  in  less  than  two  minutes  if  the  work  is  not  interfered 
with  by  the  too  close  planting  of  trees.  Smaller  trees  usually  require 
from  one  to  two  minutes,  according  to  size.  When  the  changing  poles 
are  used  (Plate  II,  figs.  1,  2;  Plate  III,  figs.  1-5)  in  covering  small 
i  rees,  one  man  on  each  side  of  the  tree  places  the  ring  over  the  end  of 
his  pole  if  catch  rings  are  used,  or  if  not,  makes  a  double  fold  of  the 
cloth  over  the  end  of  the  pole  and  makes  a  half-hitch  over  it  with  the 
rope  to  prevent  it  from  slipping  off.  With  the  pointed  end  of  the 
pole  on  each  side  about  opposite  the  center  of  the  tree  they  then  raise 
the  end  o{  t  he  pole  and  attached  tent  about  8  feet,  or  until  the  pointed 
ends  hold  without  slipping,  and,  holding  on  to  the  rope,  step  forward 
and  away  from  the  tree  and  pull  the  tent  into  position.  Some  opera- 
tor- prefer  after  attaching  the  tent  to  the  end  of  the  pole,  to  stand  with 
one  foot  on  the  pointed  end  and  raise  the  pole  entirely  by  means  of  the 
rope.  Knots  tied  in  the  ropes  at  convenient  intervals  near  the  end 
arc1  of  great  assistance  in  pulling.  If  the  trees  are  so  large  that  they 
require  tents  too  large  and  heavy  for  handling  by  two  men  and  yet 
not  large  enough  to  require  the  use  of  derricks,  a  third  man  may  be 
employed  to  advantage.     The  cd^c  of  the  tent  is  made  fast  to  the 

«  Agricultural  Journal  (^Capc  Town),  1902,  p.  4. 


28  FUMIGATION     FOB   THE   CITBTJS    WHITE    FLY. 

end  of  each  pole  as  before,  hut  the  two  operators  station  themselves 
with  the  rope  in  hand  at  the  foot  of  their  respective  poles  while  the 
helper  raises  the  end  of  each  pole  in  turn,  so  that  the  operators  can 
use  their  ropes  to  advantage.  The  committee  of  the  Clermont  Horti- 
cultural Club,  of  California,  in  their  report  heretofore  referred  to,  rec- 
ommended that  four  men,  or  two  for  each  pole,  be  regularly  employed. 
When  trees  are  close  planted  or  there  is  fear  of  breaking  branches  by 
changing  the  tent  from  one  tree  to  the  next,  or  there  is  dead  wood 
threatening  to  tear  the  tent  if  simply  dragged  off,  the  practice  of 
"skinning  it  off"  will  be  found  to  be  useful.  In  this  method  the 
attachments  of  the  poles  are  made  at  the  far  side  of  the  tent  and  the 
cloth  slides  over  itself  as  the  tent  is  pulled  from  one  tree  to  the  next. 
In  handling  sheet  tents  by  means  of  derricks  (PI.  V,  figs.  1,  2;  PL 
VI,  fig.  1)  four  to  six  men  can  work  to  best  advantage.  The  writer 
has,  however,  with  one  assistant  successfully  handled  a  sheet  with 
26-foot  derricks.  After  placing  one  of  the  derricks  in  the  position  for 
raising  the  tent  the  guy  rope  was  fastened  to  a  tree  while  the  second 
derrick  was  raised.  Each  operator  then  held  the  guy  rope  by  means 
of  a  loop  through  which  the  elbow  was  placed,  giving  the  use  of  both 
hands  while  raising  the  tent  with  the  tackle.  Ordinarily  two  men 
should  not  attempt  to  cover  a  tree  by  themselves,  particularly  if  there 
is  a  slight  breeze.  When  four  men  are  available  for  handling  sheet 
tents  with  derricks,  they  proceed  as  follows:  The  sheet  is  pulled  into 
position  back  of  the  tree  to  be  covered,  with  the  rings  located  one  on 
each  side.  The  derricks  are  placed  one  on  each  side  of  the  tree,  flat 
on  the  ground  and  their  bases  parallel,  either  directly  opposite  the 
center  of  the  tree  or  within  a  distance  of  3  or  4  feet  back,  whichever 
experience  with  trees  of  various  sizes  and  widths  of  rows  may  show  to 
be  best.  Two  men  station  themselves,  one  at  the  base  of  each  der- 
rick with  guy  rope  in  hand.  The  other  two  men  go  to  the  opposite 
ends  of  their  uprights  and  raise  them  to  a  vertical  position  with  the 
assistance  of  the  men  at  the  bases,  who  pull  with  the  guy  ropes,  stand- 
ing on  the  cross  pieces  as  long  as  necessary  to  prevent  slipping.  The 
second  two  men  now  steady  the  derricks  while  the  first  two  walk  for- 
ward and  take  a  position  for  holding  them  in  place  by  means  of  the 
guy  ropes.  The  derricks  are  now  brought  to  a  position  where  the 
tops  are  3  or  4  feet  beyond  the  vertical  in  order  to  prevent  the  weight 
of  the  guy  rope  from  causing  them  to  fall  forward  prematurely. 
The  two  men  at  the  bases  of  the  derricks  now  attach  the  hooks  of  the 
swinging  blocks  to  the  rings  of  the  tent  and  by  means  of  the  tackle 
raise  the  front  edge  of  the  tent  to  the  tops  of  the  derricks.  These 
men  may  now  tie  their  hoisting  ropes  to  the  braces  or  hold  them 
tightly  by  hand  while  the  other  men  pull  on  the  guy  ropes,  causing 
the  derricks  to  fall  forward,  pulling  the  tent  over  the  tree.  Five  or 
six  men  may  be  needed  to  cover  very^  large  seedling  trees  such  as  are 


I 


Plate  V. 


Fig.  1— Raising  33-Foot  Derricks  to  an  Upright  Position.    (Original.j 


Fig.  2.— Derricks  in  Position  iOne  on  Each  Side  of  Tree)  Supported  by  Guy 
Ropes;  Pulleys  Hooked  to  Catch-Rings  in  the  Tent.    (Original. 


:•; 


VI. 


Fig.  1.— Front  Edge  of  Sheet  Tent  Raised  to  Tops  of  Derricks,  Ready  to  be 
Pulled  Over  Tree.    (.Original.) 


Fig.  2.— Sheet  Tent  Ready  for  Introduction  of  Chemicals.    (Original.) 


mi  i  in  ins   OF    HANDLING    i  i 

common  in  Florida,  especially  when  the  tree-  are  closely   jet.     After 
adjusting  or  "kicking  in"  the  edges,  the  tent  is  read)  for  the  intro- 
duce ion  of  i  be  chemicals. 

Whether  simple  poles  or  derricks  are  used,  tents  are  usuall} 
changed  From  one  tree  to  the  next  in  the  row  b\  making  the  attach- 
ment as  described  and  pulling  the  tenl  directly  off  from  one  onto 
the  other.  When  there  are  only  a  few  large  trees  to  fumigate  and 
the  tents  ;it  hand  are  singly  not  sufficiently  large  to  cover,  two  can 
be  frequently  used  to  advantage,  placing  them  in  position  from  oppo- 
site sides  and  having  them  overlap  as  much  as  possible  without  inter- 
fering with  tightness  at  the  ground. 

li  is  best  to  have  the  tents  large  enough  so  that  not  less  than  2  feet 
of  the  edge  will  rest  on  the  ground  at  any  point  when  adjusted  and 
ready  for  fumigation.  Sometimes  it  may  be  necessary  to  weight 
down  the  tents  at  certain  points  by  means  of  a  few  shovelfuls  of 
earth.  Carelessness  of  the  workmen  charged  with  adjusting  the 
tents  at  the  ground  would  result  in  seriously  curtailing  the  benefits 
from  fumigating  a  grove.  When  arriving  at  the  end  of  a  row,  or  on 
other  occasions  when  it  is  desired  to  uncover  a  tree  without  at  the 
same  time  pulling  the  tent  in  position  over  another,  the  tent  is  usually 
dragged  off  by  hand.  If  there  is  dead  wood  present,  however,  to 
avoid  the  possibility  of  injuring  the  tent,  removal  with  the  poles  or 
derricks  may  be  advisable.  It  is  well  to  call  attention  again  to  the 
desirability  of  always  pulling  the  tent  lengthwise  with  the  strips, 
whether  in  changing  the  tent  from  tree  to  tree  or  in  dragging  off  from 
a  tree  after  treatment. 

lull  tents. — The  method  of  covering  trees  with  bell  or  hoop  tents  is 
so  plainly  shown  by  Plate  I  as  to  require  but  few  words  of  explanation. 
The  cloth  should  fall  over  .the  hoop  on  the  side  farthest  from  the  tree, 
in  order  to  bring  the  center  of  the  tent  about  over  the  center  of  the 
tree  in  covering.  Usually  two  men,  one  on  each  side,  can  easily 
throw  the  tent  entirely  over  the  tree,  but  if  the  tree  to  be  covered  re- 
quires nearly  the  full  capacity  of  the  tent  it  will  be  necessary  to  pass 
around  to  the  front  of  the  tree  and  pull  the  tent  down  into  position 
with  the  hoop  resting  on  the  ground.  Ordinarily  the  cloth  which  ex- 
tends below  the  hoop  makes  the  tent  sufficiently  tight  at  the  bottom 
when  the  hoop  is  resting  flat  on  the  ground.  An  extra  man  with  a 
pole  or  rope  may  be  necessary  to  assist  in  handling  the  largest  sizes  of 
hoop  tents,  when  they  are  used  to  cover  the  largest  trees  possible.  In 
changing  from  one  tree  to  the  next  in  the  row  a  little  experience  will 
show  what  is  the  quickest  and  easiest  method.  Tents  of  this  pattern 
are  at  present  little  used  in  California,  the  sheet  tent  being  greatly 
preferred  even  for  small  trees. 


30  FUMIGATION    FOR    THE   CITRUS    WHITE    FLY. 

MEASURING    TREES. 

Necessity  for  measurements. — The  rule  followed  by  some  California 
fumigators  in  estimating  the  dosage  for  scale  insects  is  to  give  an 
amount  which  in  the  manager's  judgment  is  as  large  as  each  tree  will 
stand  without  injury  to  well- matured  growth.  Tender  growth  is 
almost  invariably  injured  by  a  proper  dosage,  but  this  loss  is  not  con- 
sidered of  consequence.  In  Florida,  however,  there  is  usually  little  or 
no  new  growth  until  toward  the  close  of  the  season  to  which  fumi- 
gation for  the  white  fly  should  be  limited.  It  is  obviously  impos- 
sible, even  for  an  experienced  fumigator,  without  measuring,  to 
judge  of  the  size  of  trees  so  accurately  as  to  avoid  overdoses,  on 
the  one  hand,  wasting  a  small  percentage  of  the  chemicals,  and,  on 
the  other  hand,  underestimates  with  the  consequent  lack  of  effec- 
tiveness. The  difference  between  an  effective  dosage  as  a  treat- 
ment for  the  white  fly  and  one  which  would  produce  injury  to  the 
tree  is  not  large  in  many  cases, a  and  careful  estimation  of  dosage 
seems  essential  for  economy  and  success  in  fumigation  for  this  insect. 
Even  among  fumigators  considered  most  successful  in  California,  there 
is  a  wide  diversity  of  opinion  as  to  the  quantity  of  chemicals  required 
for  trees  of  the  same  size,  as  shown  by  the  observations  of  Air.  S.  J. 
Hunter,  reported  by  Professor  Woodworth,  and  by  the  published  rec- 
ommendations as  to  dosage  by  various  writers.  The  significance  of 
this  in  California  is  that  there  is  a  great  difference  between  efficiency 
against  the  scale  insects  treated  and  danger  to  the  trees;  and  the  prac- 
tice of  basing  dosage  on  guesses  as  to  the  dimensions,  either  before  or 
after  covering,  necessarily  results  in  the  danger  of  underestimation  of 
the  dosage  requirement  on  the  one  hand  and  a  needless  waste  of 
chemicals  on  the  other.  A  study  of  the  table  given  in  the  appendix, 
showing  the  dosage  recommended  for  successful  work  against  the  white 
fly  with  untreated  tents,6  proves  the  physical  impossibilit}^  of  a  fumi- 
gator approximating  such  dosage  without  a  definite  knowledge  of  the 
size  of  the  space  inclosed  and  of  the  ratio  of  the  number  of  cubic  feet  of 
contents  to  the  square  feet  of  surface  through  which  the  gas  gradually 
escapes.  This  can  be  obtained  only  by  actual  measurements.  The 
only  two  dimensions  which  it  is  at  all  practicable  to  obtain  are  the 
circumference  of  the  tented  tree  at  the  base  and  the  distance  over  the 
top  from  ground  to  ground.  The  system  here  recommended  will,  by 
insuring  satisfactory  results,  prove  the  most  economical  for  adoption 

« The  experimental  work  conducted  in  Florida  during  the  winter  of  1907-8  has 
shown  that  the  liability  of  injuring  citrus  trees  from  overdosing  is  frequently  depend- 
ent upon  the  physiological  condition  of  the  trees  as  affected  by  the  nature  of  the 
soil,  the  soil  moisture,  and  the  chemical  fertilizers  used  in  the  grove. 

h  Water-shrunk  or  its  equivalent  as  regards  tightness.  It  should  be  borne  in  mind 
that  mildew-proofing  with  tannin,  etc.,  is  not  supposed  to  increase  tightness  more  than 
does  the  normal  shrinking. 


Ml. am  RING    I  M  8  I 

1>\   ;m\   citrus  grower  contemplating  the  use  of  fumigation  for  ih<- 
white  il\ .     This  has  been  thoroughly  demonstrated  bj   the  experi 
mental  work  conducted  in  1 1  u»  winter  of  L907  s.  when,  as  has  been 
stated,  approximately  1,000  trees  were  fumigated. 

Methods  followed  in  experimental  work.  The  measurements  of 
tented  trees  in  the  experiments  conducted  in  Januarj  and  February, 
1907,  were  made  by  means  of  a  tape  measure  attached  to  a  reel.  In 
obtaining  the  distance  over  in  each  case  the  end  of  the  t.-i|><'  was  held 

in  one  hand  while  the  reel  was  thrown  over  the  center  of  the  tent  and 
the  measurement  made  from  ground  to  ground.  For  the  purposes  of 
the  experiments,  accuracy  being  desired  as  far  as  possible,  measure- 
ments were  made  in  two  directions,  from  east  to  west  and  from  north  to 
south.  In  each  case  care  was  used  to  have  the  tape  pass  as  nearly  as 
possible  over  the  center  of  the  tree  regardless  of  the  highest  point.  ( )f 
72  tented  trees  measured  in  two  directions,  70  per  cent  were  found  to 
vary  12  inches  or  less  in  the  two  measurements,  15  per  cent  to  vary 
from  13  inches  to  24  inches,  and  11  percent  from  25  inches  to  50  inches. 
The  average  variation  was  12  inches  and  the  maximum  50  inches. 
Inasmuch  as  it  is  recommended  that  in  using  the  table  appended 
hereto  the  number  in  the  first  column  next  above  the  actual  measure- 
ment (when  the  actual  measurement  is  more  than  6  inches  above  an 
even  number)  be  selected  in  estimating  the  dosage,  it  is  evident  that  in 
nearly  all  cases  a  measurement  over  the  top  of  the  tented  tree  in  one 
direction,  together-  with  the  circumference,  wall  show  the  dosage  with 
sufficient  accuracy  for  practical  purposes.  A  fumigator  should,  how- 
ever, in  using  the  table  and  knowing  the  measurement  over  in  one 
direction,  make  allowances  in  case  the  irregular  shape  of  the  tree 
makes  the  single  measurement  over  the  top  fall  short  of  indicating  the 
true  size. 

A  new  scheme  for  obtaining  measurements. — The  measuring  of  the 
tented  tree  by  means  of  the  tape,  as  described,  requires  two  men, 
owing  to  the  difficulty  of  getting  the  tape  over  the  center  of  the 
tree.  Ordinarily  it  requires  only  one  or  two  minutes  at  the  most  to 
obtain  these  measurements,  but  when  more  than  a  few  trees  are  to  be 
treated  a  simpler  and  quicker  process  is  necessary.  One  man  can 
quickly  obtain  the  circumference  by  using  a  tape  provided  at  the  end 
witli  means  for  attaching  to  the  tent,  while  he  walks  once  around  the 
tree  to  the  starting  point,  unreeling  the  tape  as  needed.  For  attach- 
ing the  tape  to  the  tent  some  form  of  metal  clamp,  such  as  is  usually 
found  in  stock  at  gentlemen's  furnishing  stores,  is  suggested.  In 
fumigating  on  a  large  scale  the  use  of  a  tape  causes  considerable 
trouble,  owing  to  unavoidable  tangling  and  misplacing,  especial  ly 
when  used  at  night.  One  of  the  operators,  however,  should  always 
estimate  the  circumference  of  the  tented  tree  by  pacing.  This  can  not 
be  done  with  sufficient  accuracy  without  considerable  prehminary 
49918— Bull.  76—08 3 


32 


FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 


^HD 


experience — obtained  by  measuring  the  first  ten  or  fifteen  trees 
covered,  both  with  the  tape  and  by  pacing,  and  comparing  the 
results.  In  pacing,  the  actual  distance  traveled  will  of  course  always 
be  greater  than  the  circumference  as  measured  by  the  tape.  With  a 
little  experience  the  proper  allowance  can  be  estimated  with  sufficient 
accuracy. 

For  obtaining  the  distance  over  the  top  of  the  tented  tree  the  author 
has  devised  a  plan  which  will  so  simplify  the  careful  estimation  of 
dosage  in  conjunction  with  tables  such  as  the  one  presented  in  the 
appendix  that  a  far  greater  uniformity  of  results  and  important  sav- 
ing of  materials  will 
follow  its  adoption. 
This  method  consists 
in  marking  the  tent 
as  shown  in  figures  6 
and  7  and  in  Plate 
VII.  The  tent  is  first 
thoroughly  water- 
shrunk,  after  which 
from  one  to  three  en- 
tire conspicuous  lines 
are  painted  length- 
wise of  the  tent  for 
the  length  of  the 
full-length  strips, 
and  one  line  at  right 
angles  to  longitudi- 
nal line  or  lines. 

For  bell  tents  and 
sheet  tents  up  to 
about  35  feet  in  di- 
ameter, one  line 
running  lengthwise 
of  the  strips  will  be 
sufficient,  although 
three  are  preferable. 
For  larger  sheet  tents  three  lines  should  always  be  made.  The  tent 
may  be  water-shrunk,  if  not  already  so,  by  allowing  it  to  become 
wet  with  dew  or  other  means,  after  which  it  should  be  thoroughly 
dried  in  the  sun.  The  entire  tent,  or  at  least  the  central  section 
of  full-length  strips,  is  spread  flat  on  the  ground,  and  the  middle 
strip  with  the  proper  location  for  a  median  line  is  located.  This 
line  should  be  painted  with  a  good  quality  of  black  paint a  (flexible 
paint  preferable)  about    2 h    or    3    inches  wide.     If  three  lines  are 


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Fig 


Diagram  showing  method  of  marking  tents  to  aid  in  obtaining 
dimensions  of  inclosed  space  when  covering  tree:  AA,  BB,  CC,  par- 
allel lines  painted  lengthwise  with  the  strips  of  cloth  from  one  • '  end ' ' 
of  the  tent  to  the  other;  DD,  cross-line  passing  through  center  of 
tent  at  right  angles  to  other  three.  [Figures  on  lines  AA,  BB,  and 
CC  represent  the  distances  in  feet  from  the  line  DD  and  figures  on 
DD  represent  distances  from  line  BB.  For  the  purposes  of  the  dia- 
gram these  distances  are  not  proportional  to  the  size  of  the  tent.] 
(Original.) 


«  Paints  containing  linseed  oil  should  be  avoided. 


: 


Plate  VII. 


Ml   VS1    RINCi     I  HI  l  S. 


88 


aeeded,  another  one  is  painted  <»n  each  Bide  of  this  line  al  b 
distance  <>i  about  36  inohes  for  tents  <»<»  feel  or  less  in  diameter 
and  from  42  to  18  inches  for  (cuts  of  larger  size.     These  two  lines 

should    not     be    more    than    I     inch    in   width.   BO    that     the\     can    be 

rcadilx  distinguished  from  the  wider  median  line.  The  exact  cen- 
ter ^\'  the  tent  is  now  located  h\  measurement  on  the  median  line 
and  the  corresponding  points  on  the  two  outside  lines  are  marked. 
Taking  into  consideration  the  smallest  tree  thai  the  tent  probably 
will  ever  he  used  to  cover,  distances  are  measured  on  these  three 
lint>s,  in  both  directions  from  the  center,  so  that  parallel  lines  about 
I  inches  long,  |  inch  wide,  and  1  fool  apart  can  he  made  across 
each  longitudinal  line,  beginning  1   foot  from  the  edge  of  the  tent 


Fig.  7.— Tent  marked  to  aid  in  estimating  dosage,  in  position  for  fumigation.     (Adapted  from 

Marlatt.) 

and  making  the  lines  in  succession  toward  the  center.  After  making 
a  given  number  of  these  cross  lines  on  each  longitudinal  line,  the 
number  in  each  case  equal  to  the  distance  from  the  middle  point  to 
the  cross  line  is  painted  on  with  conspicuous  figures.  (PI.  Ill,  figs. 
3,  4,  5,  and  6;  PL  IV,  fig.  1;  PI.  VII,  figs.  1  and  2.)  If  properly 
marked  according  to  these  directions,  the  corresponding  cross  lines 
on  the  three  parallel  longitudinal  lines  should  be  marked  with  the 
same  number,  as  shown  in  figure  6.  When  the  tent  is  exactly  cen- 
tered over  a  tree  the  reading  at  the  ground  on  both  sides  of  the  tent 
will  be  the  same.  Ordinarily,  however,  when  the  tent  is  so  placed 
that  this  line  passes  as  nearly  over  the  center  of  the  tree  as  it  is 


34  FUMIGATION    FOR    THE    CITRUS    WHITE   FLY. 

possible  to  estimate,  the  readings  will  differ  by  2  or  3  feet,  often 
more.  As  the  tent  should  always  be  pulled  lengthwise  of  the  strips, 
the  central  line  will  most  often  lie  over  the  center  of  the  tree,  and 
hence  be  most  useful  in  obtaining  the  distance  over  from  ground 
to  ground.  Frequently,  however,  this  measurement  of  the  tented 
tree  can  be  best  obtained  by  selecting  for  the  purpose  one  or  the 
other  of  the  outside  lines.  The  distance  over  the  top  in  all  cases  is 
the  sum  of  the  two  readings  on  the  line  selected.  The  fourth  line, 
painted  at  right  angles  to  the  three  running  lengthwise,  passing 
through  the  middle  point  of  each,  extending  to  the  sides  of  the  tent 
and  marked  with  the  distances  corresponding  to  those  on  the  first 
three  lines,  will  be  of  advantage  when  a  tree  is  so  irregular  in  form 
that  one  line  passing  over  the  center  of  the  tree  seems  to  fail  to  give 
the  measurement  with  sufficient  accuracy.  When  it  is  necessary  to 
use  this  line  the  tent  can  be  readily  pulled  directly  forward  or  back- 
ward whatever  distance  is  necessary  to  bring  this  line  as  nearly  as 
possible  over  the  center  of  the  tree,  leaving  the  longitudinal  line 
(previously  selected  as  the  one  passing  most  nearly  over  the  center) 
in  the  same  relative  position  as  before.  The  average  of  the  read- 
ings on  the  two  lines  will  give  the  desired  dimension  as  nearly  cor- 
rect as  is  necessary.  Measurements  of  a  few  such  irregular  trees 
will  assist  the  operator's  judgment  until  his  experience  is  sufficient 
to  enable  him  to  estimate  the  allowance  in  ordinary  cases  when 
necessary.  The  tables  appended,  however,  give  a  margin  above  the 
average  requirements  which  will  cover  ordinary  cases  of  variation 
from  the  regular  forms. 

When  a  single  longitudinal  line  is  used  on  the  smaller  sized  tents 
this  line  can  be  readily  brought  to  any  desired  position  by  pulling 
sidewise  on  the  tent,  without  the  risk  of  damage  by  ripping  at  the 
seams,  as  with  the  larger  sizes.  The  lines,  in  addition  to  their  use- 
fulness in  estimating  the  dosage,  will  be  found  of  considerable  assist- 
ance in  locating  the  catch  rings,  and  in  other  ways,  when  handling 
the  tent. 

Previously  proposed  schemes  for  marking  tents  to  aid  in  estimating 
dosage. — The  idea  of  marking  the  tents  to  aid  in  determining  the  dose 
is  not  a  new  one,  for  in  California  several  years  ago  a  tent  was  in- 
vented which  was  marked  with  concentric  rings,  at  each  of  which 
a  dose  was  indicated.  This  failed  to  take  into  consideration  the 
variation  in  circumference  of  tented  trees  whose  distance  over  is  the 
same.  Professor  Woodworth  has  suggested  a  system  of  marking 
tents,  concerning  which  he  says:  a 

It  consists  in  making  a  series  of  parallel  lines  near  two  opposite  edges  of  the  tent, 
which  are  so  distanced  from  the  center  point  that  they  shall  correspond  with  the 
dosage  of  a  tree  of  the  average  shape.     Upon  these  lines  will  be  placed  numerals, 

a  Bui.  152,  Cal.  Agr.  Exp.  Sta.,  p.  15. 


Ml  CHOD  OF   OEM  BRA  CING   TB  r   G  \    ■  85 

indicating  the  dose,  the  circumference  in  yard     pace      and  the  difference    tl 

the  amount  the  dote  muri  be  varied)  should  the  distance  around  be  i •  01  le 

than  ih»-  amount  indicated  for  an  average  tent. 

This  suggestion  in  regard  t<»  the  marking  of  tents  with  the  do 
to  obviate  the  use  of  printed  1  a  hies  seems  to  the  writer  to  be  of  con- 
siderable value  under  some  circumstances.     One  objection  i<>  the  use 
of  differentials  in  this  manner  is  that  the  cubic  capacity  and  do 

does  not    increase   in  direct    proportion   to   the   increase   in   eirnunfer- 

ence  with  a  given  distance  over  the  top.  To  illustrate  the  method 
of  marking  the  tents  with  the  dosage,  when  desired,  a  tent  meas- 
uring 30  feel  over  from  ground  to  ground  will  serve  as  an  example. 
The  table  in  the  appendix  shows  that  for  every  5  feet  of  difference 
in  the  measurement  of  the  circumference  of  a  tent  measuring  30  feet 
over  the  top.  the  amount  of  cyanid  is  increased  or  decreased  one- 
half  ounce,  or  0.1  ounce  for  each  foot.  With  the  figure  30  013  the  tent, 
we  would  place  the  dosage  of  a  tented  tree  measuring  30  feet  in  cir- 
cumference. The  dosage  called  for  by  the  table  for  a  tent  of  this 
size  (30  by  30)  is  94  ounces.  Following  this  the  differential,  or  0.1 
ounce,  is  placed.  The  entire  directions  for  obtaining  the  dosage 
would  read  30 — 9} — 0.1.  A  tented  tree  measuring  30  feet  over  and 
38  feet  in  circumference  would  require  94  ounces  plus  0.8  ounce  or, 
for  practical  purposes,  10J  ounces.  If  the  measurement  was  30  feet 
over  and  25  feet  in  circumference,  the  dosage  would  be  9J  less  0.5 
ounce,  or  9  ounces. 

When  tables  are  worked  out  in  detail,  as  they  should  be  where 
accurate  work  is  desired,  reference  to  them  is  undoubtedly  by  far 
the  quickest  and  safest  method  under  ordinary  circumstances. 

METHOD    OF    GENERATING    THE    GAS. 

In  order  to  permit  of  making  the  measurements  of  tents  and  esti- 
mating the  dosage  with  the  care  hereafter  recommended  and  with 
the  least  possible  delay,  it  is  sometimes  advisable,  in  operations  on 
a  large  scale,  that  the  cyanid  be  weighed  during  the  day  or  at  other 
times  when  it  is  not  advisable  to  fumigate,  or,  if  done  at  night,  that 
an  additional  helper  be  employed.  Such  a  helper,  in  addition  to 
weighing  the  cyanid,  might  look  after  the  replenishing  of  the  stock 
of  cyanid  and  acid  at  the  cart  as  needed  and  assist  in  measuring  the 
tents  and  emptying  the  generating  jars.  The  cyanid  should  be 
weighed  up  in  lots  of  J,  1,  2,  5,  10,  and  20  ounces,  put  into  paper 
bags  of  convenient  size,  and  protected  from  dampness.  When  the 
tented  trees  all  measure  less  than  34  feet  over  the  top  from  ground 
to  ground,  the  doses  of  20  ounces  each  will  not  be  required,  and 
when  measuring  more  than  this  the  lots  of  one-half  ounce  may  be 
dispensed  with.  At  the  cart,  drag,  or  tray  these  bags  of  cyanid 
should  be  kept  in  separate  boxes,  or  in  separate  compartments  of  a 


36  FUMIGATION    FOR   THE   CITRUS   WHITE   FLY. 

large  box,  and  selected  as  needed  to  make  up  the  proper  dosage  for 
the  trees  as  they  are  fumigated.  It  has  been  the  writer's  experi- 
ence that  the  better  plan  is  to  weigh  up  the  chemicals  in  the 
field  as  fast  as  the  dosage  for  the  successive  trees  is  determined. 
Three  times  as  many  ounces  of  water  (liquid  measure)  as  of  cyanid 
is  first  poured  into  the  jar.  It  is  unnecessary  to  be  exact  in  this 
measurement,  and  a  long-handled  dipper  of  16  ounces  or  1  pint 
capacity  is  preferable  to  the  glass  graduate.  If,  for  example,  36  ounces 
of  water  are  required,  two  and  one-fourth  dipperfuls  are  poured  into 
the  jar,  dipping  from  the  pail  carried  with  the  commissary  tray.  As 
many  ounces  of  acid  as  cyanid  to  be  used  is  measured  in  the  graduate, 
being  poured  from  one  of  the  pitchers  which  are  carried  in  one  end 
of  the  commissary  tray  (Plate  IV,  fig.  1). 

Another  member  of  the  crew  in  the  meantime  arranges  for  the 
proper  dose  of  the  cyanid  and,  with  a  lantern  in  hand  when  neces- 
sary, raises  the  edge  of  the  tent  while  the  one  who  measures  the  acid 
and  water  pours  the  acid  into  the  jar  containing  the  water,  carries 
the  cyanid  and  generating  jar  under  the  tent  (Plate  VII, fig.  2),  and  at 
arm's  length  empties  in  the  cyanid.  The  jar  should  be  placed  about 
halfway  between  the  base  of  the  tree  and  the  edge  of  the  tent.  For 
each  8  or  10  ounces  of  cyanid  the  generating  jar  should  have  a  capacity 
of  1  gallon.  For  very  large  seedling  trees  two  3-gallon,  4-gallon,  or 
even  5-gallon  jars  may  sometimes  be  needed,  while  at  other  times  one 
3-gallon  jar  and  one  2-gallon  jar  will  be  required  for  single  trees, 
although  to  avoid  errors  it  is  preferable  to  divide  the  dose  evenly 
between  the  jars  when  more  than  one  are  used.  When  two  jars  are 
used,  they  should  be  placed  one  on  each  side  of  the  tree.  The 
operator  holds  Ins  breath,  as  soon  as  the  cyanid  is  dropped  into  the 
generator,  and  as  soon  as  he  is  outside  the  edge  of  the  tent  is  dropped 
into  place,  while  the  violent  boiling  of  the  chemicals,  as  the  gas  is 
generated,  can  be  distinctly  heard  for  several  minutes.  The  cyanid 
should  be  added  as  soon  as  possible  after  adding  the  acid,  for  the 
heat  evolved  by  the  acid  and  water  at  the  time  of  mixing  is  neces- 
sary for  the  rapid  generation  of  the  gas.  The  man  who  measures  the 
acid  and  generates  the  gas  should  have  his  hands  protected  by  loose- 
fitting  rubber  gloves  and  should  avoid  being  too  close  to  the  jar 
when  pouring  in  the  acid.  He  should  never  touch  the  tent  while 
wearing  the  gloves  unless  they  have  been  thoroughly  rinsed  in  water. 

WORK    ROUTINE. 

The  systematic  arrangement  of  the  details  of  the  procedure  is  of 
great  importance  in  fumigation.  The  plans  of  work  vary  consider- 
ably with  different  fumigators,  but  it  is  the  purpose  in  all  cases  to  fol- 
low such  work  routine  as  will  keep  all  hands  constantly  employed. 
In  California  from  two  to  six  men  are  employed  in  each  outfit  accord- 


WORK    ROUTINE.  87 

1 1 1 u:  to  tli«'  size  and  Dumber  of  the  trees.  For  medium  sized  tree 
requiring  tents  not  larger  than  n  feel  in  diameter,  five  men  can  work 
to  advantage.  This  craro  can  handle  30  tents  ever}  fortj  five 
minutes  and  can  treat  from  350  to  400  trees  in  ;i  night's  work  of  ten 
hours.  For  trees  requiring  larger  tents,  which  are  shifted  by  means  of 
uprights,  a  <ivw  of  five  or  six  men  is  needed  t<>  handle  about  12  or  L5 
tents  every  forty-five  minutes,  or  between  100  and  150  trees  in  a  full 
night's  work.  This  rapidity  is  attained  when  the  trees  arc  regularly 
set  and  properlj  spaced  and  when  the  schedules  showing  the  dosage 
for  each  tree  to  be  fumigated  are  prepared  during  the  day,  or  when  the 
dose  is  based  upon  the  judgment  of  the  fumigator  after  the  tent  has 
been  placed  in  position.  As  has  been  stated,  the  plan  of  work  com- 
monly followed  in  California  in  treating  scale  insects,  as  far  as  the 
estimation  of  dosage  is  concerned,  can  not  be  recommended  for  use 
against  the  white  fly  in  Florida.  The  method  of  estimating  the 
dosage  herein  recommended  at  the  most  affects  the  schemes  of  routine 
previously  followed  in  fumigating  only  by  adding  an  extra  man  to 
the  crew.  One  man  can  calculate  the  dosage  faster  than  two  men  can 
weigh  out  t  he  chemicals  and  generate  the  gas.  The  extra  expense  of  an 
additional  man  is  entirely  negligihle  considering  the  increase  in  effi- 
ciency on  the  one  hand  and  the  check  on  unnecessary  waste  of  the 
chemicals  on  the  other. 

Barrels  of  water  should  be  placed  during  the  day  at  convenient 
points  in  the  grove,  as  should  also  carboys  or  large  jugs  containing 
the  acid.  The  tents  are  taken  to  the  end  of  the  rows,  unrolled,  and 
placed  in  position  for  covering  the  first  trees.  The  cart  with  its  sup- 
ply of  acid  and  cyanid  is  located  near  the  end  of  the  row  of  tents,  and 
everything  is  put  in  readiness  to  start  work  by  sundown  if  the  wind 
is  not  so  strong  as  to  interfere.  Each  man  in  the  crew  has  definitely 
assigned  duties.  The  men  who  handle  the  poles  or  derricks  are  com- 
monly known  in  California  as  ''tent  pullers,"  or  "tent  men."  These 
men,  with  their  one  or  more  assistants,  proceed  to  pull  each  tent  in 
succession  over  the  first  trees  of  the  row.  If  one  tree  should  be  missing, 
the  tent  is  left  unused  during  the  first  period  rather  than  to  break  the 
line  by  moving  it  at  once  to  the  second  tree.  As  each  tree  is  covered, 
each  one  of  the  tent  men,  after  disconnecting  his  pole  or  derrick,  walks 
halfway  around  the  tent,  pulling  in  the  edges  so  that  it  will  not 
spread  out  to  inclose  unnecessary  space.  A  tent  after  being  pulled 
in  at  the  bottom  is  shown  in  Plate  VI.  After  reaching  the  end  of  the 
row  the  tent  men  return  to  the  cart  or  commissary  tray  and  assist  in 
generating  the  gas.  As  soon  as  the  first  tent  is  in  position  the  fore- 
man with  a  lantern  in  hand,  except  when  the  light  from  the  moon  is 
sufficient,  notes  the  position  of  the  tent  with  respect  to  the  center  of 
the  tree,  using  as  guides  the  lines  heretofore  described.  The  reading 
is  made  where  the  selected  line  touches  the  ground. 


88  FUMIGATION   FOR   THE   CITRUS   WHITE  FLY. 

He  notes  on  the  scratch  pad  the  first  reading  and  paces  around  the 
tent,  noting  on  the  pad  the  reading  on  the  opposite  end  of  the  selected 
line.  Upon  reaching  the  starting  point  the  distance  over  and  the 
circumference — as,  for  example,  38-44 — are  noted  at  once  upon  the 
diagram  (fig.  3,  D;  figs.  4,  5).  The  dosage  table  is  referred  to  and  the 
amount  of  cyanid  to  be  given  is  noted  in  the  diagram  below  the  figures 
noting  the  dimensions.  The  foreman  or  the  man  who  determines 
the  amount  of  chemicals  then  assists  in  measuring  and  introducing 
the  chemicals,  or  if  two  other  men  are  available  for  this  work  he  pro- 
ceeds to  the  next  tree  and  determines  the  dosage  as  before. 

The  supply  of  water  and  chemicals  for  the  set  of  tents  is  moved 
ahead  as  fast  as  the  generating  of  the  gas  is  started  under  each  tree. 
The  assistant,  when  working  on  the  second  set  of  trees,  picks  up  the 
generating  jars  beneath  the  first  trees  recently  fumigated  and  midway 
between  the  rows  scoops  out  a  hole  with  his  foot  or  with  a  spade  and 
buries  the  contents  of  the  jar.  The  foreman  should  never  trust  any 
responsible  part  of  the  operation  to  an  assistant  whom  he  does  not 
know  to  be  reliable.  He  should  thoroughly  systematize  the  work  so 
that  no  unnecessary  hands  will  be  employed  while  at  the  same  time 
his  entire  outfit  of  tents  will  be  utilized  to  the  best  advantage. 

ESTIMATION   OF  TIME  REQUIRED    FOR   FUMIGATION   OF  GROVE. 

When  two  men  can  conveniently  shift  the  tents,  they  can  cover  a 
tree,  take  the  measurements,  and  generate  the  gas  without  difficulty 
in  about  five  minutes  when  not  hampered  by  irregularities  in  the 
location  of  trees.  This  means  that  two  men  should  be  able  to  handle 
9  or  10  tents  in  forty-five  minutes  with  the  methods  herein  recom- 
mended. Allowing  fifteen  minutes  each  hour  for  rest  and  restock- 
ing of  the  commissary  tray  with  chemicals,  two  men  beginning 
at  4  p.  m.  could  fumigate  about  75  trees  by  midnight.  Three  men 
in  the  same  time  could  easily  fumigate  100  or  115  trees  somewhat 
larger  in  size,  or  at  the  rate  of  13  or  14  tents  every  hour.  Four  or  five 
men  should  be  able  to  fumigate  each  hour  from  20  to  25  trees  as  large 
as  can  conveniently  be  covered  by  means  of  changing  poles.  When 
uprights  are  used  a  crew  of  six  men,  or  possibly  in  some  cases  as  many 
as  eight,  can  work  to  best  advantage.  Such  a  crew  should  handle 
from  10  to  15  tents  50  feet  in  diameter,  or  larger,  every  hour,  including 
time  for  rest  and  restocking  cart  or  tray  with  the  chemicals. 

With  three  men  attending  to  determining  the  dosage  and  generating 
the  gas  and  two  men  shifting  the  tents,  the  trees  being  12  to  15  feet 
high,  the  author  with  other  agents  of  the  Bureau  in  experimental 
work  on  one  occasion  fumigated  19  trees  in  thirty-five  minutes.  In 
one  night  a  crew  of  six  men  have  fumigated  221  budded  trees  varying 
from  12  to  16  feet  in  height.  In  this  case  certain  irregularities  in 
the  plan  of  setting  the  grove  prevented  a  much  better  record. 


APPROXIMATING   hi. mi  N8ION8    \ni>  I  UBIC   C0NT1  n  89 

In  undertaking  the  Fumigation  of  a  large  grove  the  citrus  growers 
Bhould  avoid  underestimating  the  hindrance  to  the  work  through  winds 
and  rains.  Fortunately  during  the  season  For  Fumigating  in  Florida 
there  is  comparatively  little  rainfall  in  ordinary  years.  In  the  central 
sec!  i.m  of  Florida  winds  at  night  will  ordinarily  interfere  very  little,  but 
in  Bections  near  the  coast  interference  From  this  source  may  be  more 
Frequent.  From  the  middle  of  December  until  the  middle  of  Febru- 
ary ii  is  well  to  make  allowance  for  an  average  of  two  nights  each  week 
when  Fumigation  work  will  have  to  be  suspended. 

In  fumigating  seedling  trees  30  feet  or  more  in  height  one  could 
expect  to  Fumigate  From  300  to  inin  rees  a  week  with  an  outfit  of  8  or  10 
tents,  [n  fumigating  trees  from  15  to  20  feel  high  with  an  outfit  of  20 
tents  one  could  expect  to  fumigate  from  800  to  1 ,000  trees  a  week.  In 
the  cases  of  both  the  large  and  the  small  trees  these  estimates  can  fre- 
quently be  exceeded  when  conditions  are  favorable,  but  as  the  period 
for  fumigating  is  so  limited  it  is  advisable  to  avoid  underestimating 
the  time  required  to  complete  the  fumigation  of  a  grove.  In  plan- 
ning for  the  necessary  equipment  it  is  safe  to  calculate  that  with  one 
tent  for  each  100  trees  the  work  of  fumigation  can  be  completed  in 
between  ten  and  fourteen  nights'  work.  In  many  cases  it  is  neces- 
sary to  have  two  complete  outfits  at  work  in  the  same  grove  when 
the  work  is  started  late  in  the  season  and  there  is  danger  of  new 
growth  appearing  on  the  trees    before  one  outfit  could   finish  the 


METHODS    OF   COMPUTING   APPROXIMATE   DIMENSIONS   AND 
CUBIC  CONTENTS. 

The  dosage  recommended  in  the  table  given  in  the  appendix  is  based 
upon  detailed  records  of  100  trees  fumigated  by  the  writer  and  his 
assistants  during  January  and  February,  1907.  Heretofore  tables  of 
this  kind  have  been  based  on  the  height  and  diameter  of  the  trees, 
with  the  exception  of  one  prepared  by  Prof.  C.  W.  Woodworth,  who 
first  recommended  a  dosage  system  based  on  the  dimensions  of  the 
tented  trees.  The  two  dimensions  of  practical  importance  are  the 
circumference  and  the  distance  over  the  top  from  ground  to  ground. 
The  method  for  obtaining  these  dimensions  has  been  described.  In 
Professor  TVoodwortlrs  table  of  dosage  referred  to  above,  the  amount 
of  <van  id  was  directly  proportional  to  the  cubic  contents.  The  table 
of  dosage  here  recommended  is  based  upon  actual  experience  and  is, 
as  far  as  known  to  the  writer,  the  first  to  take  into  consideration  the 
effect  of  leakage.  Tented  trees  are  always  more  or  less  irregular  and 
any  attempt  to  calculate  the  volume  of  the  space  inclosed  can  give 
only  approximate  figures.  A  cylinder  surmounted  by  a  hemisphere 
is  the  regular  figure  that  is  nearest  to  the  form  of  a  tented  tree.  The 
leakage  surface  of  a  flat  octagonal  tent  covering  a  tree  obviously  is  not 


40  FUMIGATION    FOR   THE   CITRUS   WHITE   FLY. 

the  same  as  the  surface  area  of  such  a  figure,  but  rather  the  area  of  a 
circle  with  a  diameter  equal  to  the  distance  over  the  top  of  the  tent 
from  ground  to  ground.  To  a  certain  extent  the  folds  in  a  tent  when 
in  position  over  a  tree  reduce  this  surface,  but  this  is  a  factor  of  little 
consequence,  as  it  is  present  in  all  cases,  and  the  portion  of  the  tent 
folded  so  as  to  prevent  all  leakage  represents  only  a  small  percentage  of 
the  whole.  For  practical  purposes,  therefore,  the  leakage  surface  is 
calculated  from  the  mathematical  formula  3.1416  multiplied  by  the 
square  of  the  radius  or  ttR2.  The  approximate  height  of  the  tented 
tree  can  be  calculated  from  the  following  formula,  in  which  C  repre- 
sents the  circumference  of  the  tent  at  the  base  and  O  represents  the 

tt     Vjn     O-C/2 
distance  over  the  top :  H  =  —~-  + ~  — 

The  diameter  is  found  by  dividing  the  circumference  by  3.1416. 
The  height  and  diameter  having  been  obtained,  the  cubic  contents  of 
the  regular  figure  mentioned  can  be  calculated  by  the  following  for- 
mula :  7rR2  (  H  —  -o   )  •    The  actual  cubic  inclosure  of  a  tented  tree  will 


(»-f> 


obviously  always  be  more  or  less  smaller  than  the  regular  figure  to 
which  this  formula  applies,  although  irregularities  in  shape  will  have 
a  tendency  to  counteract  one  another. 

DOSAGE  REQUIREMENTS  FOR  THE  WHITE  FLY. 
EXPERIMENTS    WITH    SHEET    TENT. 

Summary  of  results  with  regard  to  dosage. — In  experiments  to 
determine  the  dosage  requirements  for  the  white  fly  when  using 
sheet  tents,  detailed  records  were  made  concerning  each  tree  fumi- 
gated during  the  first  season's  work,a  including  every  factor  which 
might  influence  the  results.  The  main  objects  in  view  in  conducting 
the  experiments  were  to  determine  the  minimum  dosage  require- 
ments for  destroying  the  white  fly  larvae  and  pupae,  the  rate  of  leakage 
of  the  gas  through  the  cloth,  the  effect  of  moisture  on  efficiency  of  the 
treatment,  the  effect  of  the  treatment  upon  the  foliage  under  various 
conditions  of  moisture,  the  margin  as  to  dosage  between  effective 
treatment  for  the  insect  and  danger  to  the  tree,  and  the  effect  of 
different  proportions  of  water  and  acid.  Observations  on  other 
points,  such  as  effect  of  wind,  sunlight,  condition  of  foliage  as 
affected  by  drought,  etc.,  were  made  as  opportunity  afforded.  All 
the  experiments  were  conducted  between  January  12  and  March 
1,  1907,  inclusive,  but  observations  as  to  results  were  continued  for 
several  weeks  after  the  latter  date.     During  this  period  practically 

a  The  results  of  the  experimental  work  during  the  winter  of  1907-8  substantiate  the 
conclusions  derived  from  the  work  of  the  first  season  so  far  as  the  data  up  to  this  time 
completed  show. 


D08AG1     REQUIREMENTS.  4  1 

all  the  immature  white  flies  were  in  the  pupal  stage.  Of  the  many 
thousands  of  specimens  examined  in  ili<'  course  «>l  the  experiments, 
lt^>  than  five  were  in  earlier  stages.  The  principal  experiments 
were  conducted  in  the  grove  at  the  laboratory  in  Orlando,  Fla., 
t mi t  cooperative  experiments  were  conducted  <>n  a  larger  scale  in  an 
extensive  grove  in  the  western  portion  of  Orange  County.  The 
detailed  records  concerning  the  efficiency  of  fumigation  against 
the  white  IK  refer  to  experiments  conducted  at  Orlando.  A  group 
of  trees  was  selected  for  treatment  on  aeeonnt  of  the  comparative 
abundance  <>(  the  live  insects.  As  it  was  considered  desirable  to 
examine  t  he  insects  both  before  and  after  treatment,  leaves  were 
selected  at  various  distances  from  the  ground,  and  in  various  sections 
of  the  tree,  and  the  number  of  live  and  apparently  normal  pupa' 
was  noted  on  a  tag  which  was  left  attached  to  each  leaf.  After 
fumigation  examinations  were  made  at  intervals  of  a  few  days  until 
the  appearance  of  the  pupae  on  the  tagged  leaves  showed,  beyond 
doubt .  that  the  insects  were  dead  or,  if  unaffected,  until  the  evidences 
of  normal  vitality  were  unmistakable  or  the  adult  insects  had  emerged. 

The  acid  used  in  the  experiments,  with  the  exception  of  experiments 
Xos.  45.37,  60.21,  X.7,  andX.8,  was  tested  with  a  Beaume  hydrometer 
and  found  to  be  66°,  as  guaranteed  by  the  manufacturers.  The 
potassium  cyanid  was  guaranteed  to  be  99  per  cent  pure.  A  sample 
was  analyzed  in  the  Bureau  of  Chemistry  of  the  Department  of 
Agriculture  and  it  was  reported  to  contain  40.59  per  cent  cyanogen, 
a  little  more  than  0.5  of  1  per  cent  more  than  that  theoretically 
present  in  chemically  pure  potassium  cyanid,  the  excess  being  due 
to  a  trace  of  sodium  cyanid. 

As  has  been  previously  stated,  the  sheet  tent  used  was  made  of  the 
brand  of  8-ounce  duck  which  is  most  used  in  California  for  fumigat- 
ing tents.  The  tent  was  untreated  but  was  thoroughly  shrunk  by 
exposure  to  heavyr  dews  and  therefore  as  tight  as  those  ordinarity 
used. 

A  system  of  numbering  the  experiments  was  adopted  which 
indicates  the  length  of  exposure  and  consecutive  number  of  the  tree 
treated  for  the  particular  duration  of  time.  The  number  before  the 
decimal  point  indicates  this  exposure  for  sixty  minutes  and  less. 
Exposures  ranging  from  one  and  a  half  to  three  hours  are  indicated  by 
the  letter  X  preceding  the  decimal  point. 

Table  IV  summarizes  the  data  based  upon  the  experiments  of 
January  and  February,  1907,  concerning  dosage  for  the  white  fly, 
including  for  convenience  the  dosage  called  for  by  the  tables  found  in 
the  appendix. 


42 


FUMIGATION    FOR   THE   CITRUS   WHITE   FLY. 


Table  IV. — Summary  of  dosage  experiments  with  sheet  tent  constructed  of  8-ounceduck. 


Measurements  of 

Amount  of 

tented  tree. 

cyanid 

recom- 

Experi- 
ment No. 

Amount  of 

Per  cent  of 

mended  in 

cyanid 

white  flies 

table  givfcn 

Distance 

Circumfer- 

used. 

destroyed. 

in  appen- 

over. 

ence. 

dix;  45 
minutes' 
exposure. 

Feet. 

Feet. 

Ounces. 

Ounces. 

20.1 

45 

57 

16! 

91.9 

29! 

30.1 

50 

60 

7 

31 

3.v 

30.2 

44 

58! 

11 

... 

28" 

30.4 

47 

62 

18 

92 

33 

30.5 

39 

50 

16! 

98.6 

20 

30.6 

46 

56 

20 

71 

29 

30.7 

40! 

56 

30 

100 

24 

30.8 

38 

48 

25f 

100 

18! 

40.1 

44 

.53 

5 

31 

25* 

40.2 

41! 

59 

10 

84 

26 

40.3 

42* 

60 

15 

85 

27 

40.4 

45 

56 

21 

80 

28! 

40.6 

39 

54 

17! 

88 

21 

40.8 

44* 

58! 

17J 

97 

29! 

40.9 

43! 

56 

12 

93 

27 

40.10 

38 

46 

13* 

95.7 

17! 

40.11 

45! 

63 

25" 

99.2 

32! 

40.12 

51! 

64 

30§ 

98.4 

41 

40.13 

44| 

57 

24 

100 

28 

40.14 

43! 

54 

26i 

100 

26 

40.15 

37 

48 

21 

100 

18 

40.18 

43 

54 

32 

100 

25 

40.20 

43 

60 

32 

100 

27 

40.21 

47! 

56 

38 

100 

31 

45.1    . 

37 

47 

21 

100 

17} 

45.3 

47 

51! 

22 

99.5 

28 

45.4 

45 

57! 

23 

100 

28 

45.5 

46! 

60! 

26! 

98.9 

32 

45.6 

43! 

56 

22! 

100 

26! 

45.7 

50! 

56 

36 

100 

34 

45.8 

44! 

58 

27 

100 

28 

45.9 

36! 

48 

21 

100 

17 

45.10 

45! 

67 

35 

100 

34 

45.12 

34! 

43 

15f 

100 

14 

45.13 

31! 
40! 

38 

11! 

100 

li! 

45.15 

50 

261 

+99.  6(?) 

21 

45.17 

37 

45 

21 

100 

16! 

45.19 

31! 

39 

14i 

100 

li! 

45.  20 

33" 

50 

12! 

99.5 

15 

45.21 

31 

42 

9 

89.3 

11 

45.22 

38 

46 

13f 

99.8 

18 

45.23 

46! 

56 

29! 

100 

29! 

45.24 

34* 
48! 

47 

15* 

100 

15 

45.25 

57 

33! 

100 

32 

45.26 

33 

46 

13 

100 

14 

45.27 

46! 

65 

a 

+99.7(7) 

34 

45.28 

46! 

50 

99.5 

26! 

45.30 

29! 

30 

6 

100 

9! 

45.33 

34! 

36 

10 

100 

14 

45.34 

40* 

44 

21 

100 

19! 

45.35 

40| 

47 

•       20 

100 

19! 

45.36 

45 

50 

20! 

97.7 

25* 

45.37 

35 

50 

191 

92 

16! 

50.1 

44 

58 

23 

66 

28 

50.2 

39! 

46* 

28 

100 

19 

50.5 

52 

56" 

37 

100 

35! 

60.1 

51 

60! 

30! 

98.6 

38 

60.2 

43 

56 

22 

100 

26! 

60.4 

44* 

58 

23! 

100 

29 

60.5 

38! 

50 

16! 

100 

20 

60.6 

33! 

38 

8! 

97 

13 

60.7 

38! 

56 

18 

94 

22! 

60.19 

41! 

58* 

27! 

100 

26! 

60.20 

29 

37* 

8! 

66 

10 

60.21 

41 

55 

25 

97.6 

24 

X.l 

43! 

56 

22! 

96.7 

26! 

X.3 

47! 

54 

28! 

99.6 

30 

.    X.4 

34 

49 

15 

99.8 

15! 

X.5 

47! 

54 

24! 

99.7 

30 

X.6 

45! 

53 

171 

98.8 

27} 

X,7 

49 

62 

40 

a99.8 

37 

X.8 

52! 

64 

35* 

6  94 

42 

a  One  pupa  apparently  alive  24  davs  after  fumigating;  738  dead. 
b  200  examined;  188  killed,  12  alive. 


DOSAG]     REQl   m;i  \l  I  N  I 


Lfl 


Deductions  concerning  effectivt  dosage.  In  formulating  a  definite 
table  of  dosage  requirements  From  the  above  experiments  the  most 
significant  results  are  those  in  which  the  amount  of  cyanid  used  was 
sufficient  to  destroy  .-ill  l>ni  a  v«t\  small  percentage  of  the  insects. 
Table  V  ghtes  more  complete  data  concerning  the  foregoing  experi- 
ments, m  which  from  ('">  to  99.9  per  cent  of  the  insects  were  killed: 
also,  for  comparison,  it  gives  the  dosage  called  for  I>\  tables  pre- 
pared l>\  t be  aut hor. 

Tabi  :    V      Data  concerning  dotage  in  those  experiments  in  which  95  to  ■  ■  tnt  of 

white  flics  a  i  rt  destroyed. 


•  riit'iits 

Expert 

of  tented  tree. 

meal 

Dia 

Cir- 

tance 

cumfer- 

ence. 

40.  10 

38 

U 

in.  s 

44! 

.>'. 

40.  11 

63 

40.  12 

51 J 

M 

46.20 

.Mi 

38 

46 

i:, 

50 

50 

47 

50j 

60.6 

33* 

38 

41 

55 

60.1 

:>1 

bX.4 

34 

49 

cX.  1 

dX.fi 

53 

«X.o 

54 

/X.3 

«1 

54 

Approx- 
imate 

capacity 
ol  In- 
closed 


cu.  ft. 

:  lis 
2.080 
3,584 

1   ."in 

1 .  862 
2,080 

3.  H»4 
1,238 
3.397 
1.297 
3.027 
4.867 
1,890 
3,412 
3.272 
3.713 
3.713 


Approx- 
imate 

Burfai  e 


Sq.  i'. 
1.07.-, 
1,134 
1 .  554 

1 .  625 
2,082 

855 
1.134 
1,590 
1,697 
1,697 
1.734 

881 
1,320 
2,042 

908 
1 .  485 
1 .  .12.-. 
1.771 
1.771 


Amount 

Kali"  "i 

Rate: 

cyanid 

Number 

leakage 

Amount 

Number 

recom- 

cubic bet 

surface 

cyan  id 

cubic  feel 

mended 

[mt  ounce 

to  cubic 

used. 

per  ounce 

in  table 

cyanid    | 

contents. 

cyanid. 

given  in 

recom-    ' 

appendix 

mended.  ' 

Ounce  . 

Ounces. 

1  : 2.  28 

148 

20 

122 

L:1.83 

13! 

1.-4 

17i 

119 

1:2.30 

17i 

207 

29 

123 

i     1:2.65 

25 

171 

32J 

L31 

1:2.56 

30| 

174 

41 

130 

1     1:2.17 

m 

149 

I.", 

124 

1:1.83 

1.1! 

1.-.4 

17J 

119 

i     1:1.88 

m 

14s 

25 

122 

!     1:1.88 

24! 

130 

120 

1:2.49 

2.U 

160 

32 

132 

1:1.95 

22 

154 

_'s 

121 

1:1.47 

8j 

152 

13 

100 

1:2.29 

o  2.". 

121 

24 

126 

1:2.38 

30! 

160 

38 

128 

1:2.08 

15' 

126 

122 

1:2.29 

22! 

156 

129    ! 

1:2.01 

17i 

189 

27* 

119 

1:2.09 

24! 

151 

30 

123 

1:2.09 

28£ 

130 

30 

123 

I 

a  One  of  several  trees  fumigated  on  night  of  March  1, 1907. 
to  poor  quality  of  acid. 
t>  Exposure,  1  hour  and  45  minutes, 
c  Exposure,  2  hours  and  50  minutes. 
d  Exposure,  1  hour  and  30  minutes. 
e  Exposure,  1  hour  and  3.5  minutes. 
/Exposure,  1  hour  and  55  minutes. 


Unsatisfactory  results  supposed  to  be  due 


For  purposes  of  comparison  with  Table  V,  the  data  on  the  dosage 
experiments  in  which  all  of  the  insects  were  believed  to  have  been 
killed  in  forty-five-minute  exposures  are  given  in  Table  VI,  which, 
like  the  preceding,  includes  the  rate  and  amount  of  dosage  calculated 
according  to  the  dosage  recommendations  hereinafter  given. 


44 


FUMIGATION    FOR    THE    CITRUS    WHITE   FLY. 


Table  VI. — Data  concerning  dosage  in  those  experiments  in  which  100  per  cent  of  white 

jlies  were  destroyed. 


Experi- 
ment 
No. 

Measurements 
of  tented  tree. 

Approx- 
imate 

Approx- 
nnate 
leakage 
surface 

Ratio  of 
leakage 
surface 

Amount 
cyanid 

Rate: 
Number 
cubic  feet 

Amount 
cyarnd 

Rate: 
Number 
cubic  feet 
per  ounce 

Dis- 

Cir- 

capacity 
of  in- 

recom- 
mended 

(series 
45). 

tance 
over. 

cumfer- 
ence. 

closed 
space. 

to  cubic 
contents. 

used. 

per  ounce 

cyanid. 

in  table 
given  in 
appendix 

cyanid 
recom- 
mended. 

Feet. 

Feet. 

Cu.  ft. 

Sq.  ft. 

Ounces. 

Ounces. 

30 

29£ 

30 

735 

683 

1:1.08 

6 

118 

9* 

77 

13 

31 

38 

1,149 

754 

1:1.52 

Hi 

100 

11 

104 

19 

31J 

39 

1,219 

779 

1:1.66 

14i 

84 

Hi 

106 

26 

33 

46 

1,656 

855 

1:1.93 

13 

127 

14 

118 

33 

34* 

36 

1,224 

935 

1:1.31 

10 

122 

13 

94 

12 

34£ 

43 

1,620 

935 

1:1.73 

15J 

103 

14 

116 

24 

34£ 

47 

1,855 

935 

1:1.98 

15^ 

119 

15J 

119 

17 

36| 

45£ 

1,888 

1,043 

1:1.81 

21 

90 

17" 

111 

9 

36§ 

48 

2,049 

1.043 

1:1.96 

21 

98 

17 

120 

1 

37 

47 

2,075 

1,075 

1:1.93 

21 

99 

17 

122 

34 

40 

44 

2,092 

1,256 

1:1.66 

21 

100 

18i 

113 

35 

40 

47 

2,341 

1,256 

1:1.86 

20 

117 

20 

117 

6 

43J 

56 

3,412 

1.482 

1:2.35 

22J 

151 

26i 

129 

8 

44* 

58 

3,691 

1,554 

1:2.37 

27 

136 

29i 

125 

4 

45 

57i 

3,732 

1,589 

1:2.34 

23 

162 

m 

131 

10 

45J 

67 

4. 665 

1,625 

1:2.87 

35 

133 

341 

132 

23 

46§ 

56 

3.556 

1,697 

1:2.15 

29§ 

124 

30 

118 

25 

48| 

57 

4,095 

1.846 

1:2.21 

33i 

122 

33 

124 

7 

50| 

56 

4,275 

2,002 

1:2.13 

36 

119 

34 

125 

These  tables  show  that  with  tents  of  8-oimce  duck  and  untreated 
with  paint  or  sizing  there  is  little  or  no  advantage  in  exposures  of 
more  than  40  minutes.  The  results  with  exposures  of  30  and  40 
minutes  compare  favorably  with  those  ranging  from  45  minutes  to 
2  hours  and  50  minutes.  It  is  evident  that  the  gas  escapes  rapidly 
and  that  in  the  course  of  a  period  of  30  to  40  minutes  at  the  most 
the  gas  from  a  dosage  of  maximum  utility  is  so  diluted  as  to  be 
practically  ineffective.  On  the  other  hand,  the  table  shows  con- 
clusively that  the  experiments  afford  no  justification  for  reducing  the 
dosage  on  account  of  lengthening  the  exposure  from  45  to  60  minutes 
or  longer.  Everything  considered,  the  writer  adopted  the  40-minute 
period  of  exposure  as  probably  affording  the  greatest  benefit  from  a 
given  amount  of  cyanid. 

As  an  aid  in  determining  the  rates  of  dosage  which  could  be  safely 
recommended  for  the  various  ratios  of  leakage  surface  to  cubic  con- 
tents, the  experiments  referred  to  in  Table  V  were  arranged  in  accord- 
ance with  the  ratio,  and  in  each  case  the  writer  estimated  the  amount 
of  potassium  cyanid  which  it  seemed  evident  would  have  been  ample 
for  the  destruction  of  all  the  insects.  The  degree  of  success  obtained 
with  the  amount  of  potassium  cyanid  actually  used  was  taken  into 
consideration  in  estimating  the  amount  needed.  The  data  thus 
arranged,  together  with  calculations  of  the  rate,  or  number  of  cubic 
feet  of  space  per  ounce  of  potassium  cyanid,  are  given  in  Table  VII. 


DOSAGE    REQ1  ii;i..m  i.N  i>. 
Tabli    VII.     Study  of  doaagt  rates. 


\:> 


tiool 

\  tii"  -mil 

Niii 

ilx  r  ciiliir- 

cyanld 

i.  .  i     ,,i 

|MT 

iii  leal 

surd 

V in. >t i lit  o( 

mid 

Peroenl  ><( 

u luir  Qiea 

Hint' 

ouooe  "i 

yanld. 

111   CI 

oublc 

UM'-I. 

deal  royed. 

raooeuful 

i    ed. 

OMltrllts. 

results. 

On  a 

Own 

1:3. 6fi 

25 

27 

171 

l.Vi 

1:2.68 

96.  I 

174 

167 

98,9 

29 

l-.ii 

1 1-, 

33 

L60 

in 

17J 

97 

20 

2U7 

179 

1:2.39 

25 

28 

127 

IMS 

I   2.28 

It.1. 

19 

Its 

128 

1:2.  17 

L2J 
24] 

14 

1 I'.l 

133 

1:2.09 

99.  7 

27 

15] 

138 

1:2.09 

99  6 

30 

130 

124 

1:2.08 

L5 

99.8 

L6 

L26 

lis 

1:2.01 

n\ 

20 

L89 

L63 

1:1.95 

22 

99.5 

24 

I.-.4 

141 

L:l.  88 

20| 

99.5 

27 

L30 

118 

L:l.  88 

97.  7 

24 

148 

127 

1:1.83 

13* 

99.8 

15 

154 

138 

1:1.83 

m 

95.  7 

17 

L46 

122 

1:1.  17 

8J 

97 

11 

152 

Us 

From  a  study  of  the  data  in  the  Table  VII  the  writer  concluded 
that  for  a  ratio  of  1:1.5  the  cyanid  should  be  used  at  a  rate  very 
near  to  1  ounce  to  110  cubic  feet  of  space.  Owing  to  the  fact  that 
in  all  cases  tented  trees  include  less  inclosed  space  than  would  a 
regular  figure  which  for  purposes  of  approximate  calculations  has 
been  considered  as  equivalent,  this  rate  would  be  higher  for  a  reg- 
ularly shaped  inclosure  whose  cubic  contents  could  be  definitely  cal- 
culated. Probably  1  ounce  to  100  cubic  feet  of  space  is  nearer  the 
actual  rate  which  the  experiments  indicate  is  necessary  with  the  ratio 
mentioned.  This,  however,  is  of  little  consequence  in  dealing  with 
sheet  tents,  for  only  the  comparative  volumes  and  dosage  rates  for 
trees  of  different  dimensions  are  required  for  practical  purposes. 
Saving  decided  upon  the  adoption  of  1  ounce  of  potassium  cyanid 
per  110  cubic  feet  of  space  with  the  ratio  of  1:1.5,  calculations  were 
made  for  tents  with  different  ratios  up  to  1:3.6.  Professor  Gossard 
reports"  that  1  ounce  to  170  cubic  feet  of  space  destroys  all  white 
fly  pupa>  in  an  air-tight  fumigatorium.  Considering  that  this  rate 
is  approximately  correct,  an  equivalent  rate  for  the  volume  inclosed 
by  a  sheet  tent  covering  a  tree  would  be  more  than  170  cubic,  feet  in 
the  ideal  form  of  inclosure  upon  which  the  calculations  are  based. 
Experiments  numbered  X.3  and  X.4,  however,  show  that  a  rate  not 
less  than  1  ounce  for  126  cubic  feet  of  space  should  be  used  when 
the  ratio  is  1 :2.  When  the  ratio  is  increased  from  1 : 1.5  to  1 :  infinity6 
and  the  rate  of  dosage  for  this  latter  ratio  is  considered  as  1  ounce 

«Fla.  Exp.  Sta.  Bui.  67,  p.  652. 

&  It  is  evident  thai  it  the  number  of  cubic  feet  of  space  were  infinitely  greater  than 
the  number  of  square  feet  of  leakage  surface,  the  rate  of  dosage  required  for  an  air- 
tight himigatorium  would  be  sufficient. 


46 


FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 


for  170  cubic  feet  of  space,  all  of  the  rates  are  more  or  less  greater 
than  those  used  in  the  experiments  in  which  from  95  per  cent  to 
99.9  per  cent  of  the  insects  were  killed.  It  is  evident  that  the  increase 
in  number  of  cubic  feet  per  ounce  of  potassium  cyanid  from  110  to 
170  must  be  calculated  at  a  rate  which  is  in  direct  proportion  to  the 
percentage  of  increase  in  cubic  contents.  The  method  employed  in 
these  calculations  is  shown  in  Table  VIII,  which  gives  the  figures 
with  the  ratios  ranging  from  1:1.0  up  to  1 :3.6. 

Table  VIII. — Rates  of  dosage  as  affected  by  ratio  of  numlx  r  of  square  fat  in  surface  to 
the  number  of  cubic  fit  in  volume. 


Per  cent 

Number 

Differ- 
ence be- 

Increase 

Per  cent 

Number 

Differ- 
ence be- 

Increase 

of  in- 

of cubic 

tween 

ber  cubic 
feet  per 

of  i  n- 

of  cubic 

tween 

in  num- 
ber cubic 
feet  per 

Ratio. 

crease  in 
cubic  con- 

feet per 
ounce 

number 
cubic  feet 

Ratio. 

crease  in 
cubic  con- 

teel per 

ounce 

number 
cubic  feel 

tents. 

cyanid. 

per  ounce 
and  170. 

cyanid. 

tents. 

cyanid. 

per  ounce 
and  170. 

ounce 
cyanid. 

1:1 
1:1.1 

76.8 
86.1 

93.2 
83.9 

1:2.4 
1:2.5 

4.34 
4.16 

133.5 
135 

36.5 
35 

1.7 
1.5 

10 

9.3 

1:1.2 

9.09 

93.7 

76.3 

7.6 

1:2.6 

4 

136.4 

33.6 

1.4 

1:1.3 

8.33 

100.1 

69.9 

6.4 

1:2.7 

3.85 

137.7 

32.3 

1.3 

1:1.4 

7.69 

105.4 

64.6 

5.3 

1:2.8 

3.7 

138.9 

31.1 

1.2 

1:1.5 

7.14 

110 

60 

4.6 

1:2.9 

3.6 

140 

30 

1.1 

1:1.6 

6.66 

114 

56 

4 

1:3.0 

3.44 

141 

29 

1.03 

1:1.7 

6.25 

117.5 

52.5 

3.5 

1:3.1 

3.33 

142 

28 

.97 

1:1.8 

5.88 

120.6 

49.4 

3.1 

1:3.2 

3.26 

142.9 

27.1 

.91 

1:1.9 

5.55 

123.3 

46.7 

2.7 

1:3.3 

3.12 

143.8 

26 

.85 

1:2.0 

5.26 

125.8 

44.2 

2.5 

1:3.4 

3.03 

144.5 

25.4 

.79 

1:2.1 

0 

128 

42 

2.2 

1:3.5 

2.94 

145.3 

24.7 

.75 

1:2.2 

4.76 

130 

40 

2 

1:3.6 

2.86 

146 

24 

.71 

1:2.3 

1 

4.54 

131.8 

38.2 

1.8 

In  Table  VIII  the  number  of  cubic  feet  of  space  per  ounce  of  potas- 
sium cyanid  increases  toward  170,  representing  the  rate  when  the 
ratio  is  1  to  infinity,  and  the  dosage  increases  in  rate  (=  decrease  in 
the  number  of  cubic  feet  per  ounce  of  potassium  cyanid)  as  the  units 
of  cubic  contents  become  infinitely  small  in  number  as  compared 
with  the  units  of  square  measure  of  leakage  surface.  Using  the 
above  rates  as  a  basis,  the  doses  for  trees  measuring  from  10  to  76 
feet  over  the  top  have  been  calculated.  The  dimensions  of  the  tented 
trees  and  volumes  of  the  inclosed  spaces  have  been  calculated  in 
accordance  with  the  formulae  given  in  the  preceding  pages.  Table  IX 
gives  the  original  calculations,  while  in  the  appendix  the  recommended 
doses  alone  are  given,  in  a  form  'more  convenient  for  practical  use  in 
the  field. 


DOSAGE    REQ1  IR]  M  EH  fS. 


rt 


Table  [X.     Recommended  dotage,  with   15-minuUexpo 


\l.\iMiivm.-iil  -  .'l 

tented  1  n  i 

u-'.i  Of 

Helghl 

of  regular 

Qgure 

1  M.mi.'l.M 

(lirure 

R 

Dumber 

Unounl 
i'f  cyanid 

•  urtaoe. 

wiiii          with 
foregoing  foregoing 

measure    m< 

\    lllllllll'. 

to  cubic 
contenl 

cubic  feel 
ounce 

Distance 

lirriiiti 

recom 
mended. 

over. 

ferenoe. 

iiinils. 

nu-iit  - 

cyanld 

8q.  feet. 

Fed 

Cu.  /<<'- 

10 

18 

7s 

i  . 

i^ 

1:0.61 

1.0 

90 

78 

3.  2 

6  i 

69 

l  ,i  89 

1.0 

ia 

i:. 

113 

i  a 

i  B 

2.0 

90 

118 

i  -■ 

0  I 

ID! 

2.0 

14 

IS 

154 

5.6 

4.8 

1:().  .V, 

90 

l. VI 

5.  2 

a  i 

L33 

in  86 

9fi 

L54 

17 

8,0 

171 

1:1.  11 

"70" 

2.  5 

16 

90 

201 

ti.  4 

165 

1:0.82 

62 

25 

201 

5.7 

8.0 

221 

1:1.  10 

- 

3.0 

"in 

201 

:,  3 

:•. :. 

976 

1:1.37 

loo 

3.0 

18 

90 

954 

7.2 

6.4 

197 

1:0.77 

:,., 

1.0 

25 

95 1 

6.7 

8.0 

27! 

1:1.00 

71 

4.0 

30 

95 1 

6,3 

9.5 

347 

1:1.36 

102 

4.0 

ss 

254 

5.8 

11.  1 

tin, 

1:1.00 

114 

4.0 

90 

90 

314 

8.2 

6  1 

229 

1:0.73 

:.l 

L2 

95 

314 

7.7 

8.0 

321 

1:1.02 

76 

12 

30 

314 

7.3 

9.5 

418 

1:1.33 

100 

4.2 

35 

314 

6.8 

11.1 

500 

1:1.59 

112 

4.4 

22 

95 

380 

8.7 

8.0 

372 

1:0.97 

75 

4.9 

30 

380 

8.3 

9.5 

489 

1:1.28 

96 

5.1 

35 

380 

7.8 

11.1 

594 

1:1.56 

111 

5.3 

40 

380 

7.4 

12.  7 

070 

1:1.78 

118 

5.9 

24 

30 

452 

9.3 

'.).  5 

550 

1:1.21 

93 

5.9 

35 

452 

8.8 

11.1 

688 

1:1.52 

110 

6.2 

40 

452 

8.4 

12.7 

797 

1:1.76 

117 

6.8 

45 

452 

7.9 

14.3 

927 

1:2.05 

128 

7.2 

26 

30 

531 

10.3 

9.5 

621 

1:1.17 

89 

7.0 

35 

531 

9.8 

11.1 

782 

1:1.47 

107 

7.3 

40 

531 

9.4 

12.7 

924 

1:1.74 

118 

7.8 

4o 

531 

8.9 

14.3 

1,046 

1:1.97 

124 

8.4 

28 

30 

615 

11.3 

9.  5 

692 

1:1.12 

86 

8.1 

35 

615 

10.8 

11.1 

876 

1:1.42 

105 

8.3 

40 

615 

10.4 

12.7 

1,051 

1:1.70 

117 

8.9 

45 

615 

9.9 

14.3 

1,206 

1:1.96 

124 

9.7 

30 

30 

707 

12.3 

9.5 

763 

1:1.08 

80 

9.0 

35 

707 

11.8 

H1.1 

970 

1:1.37 

100 

9.7 

40 

707 

11.4 

12.7 

1,178 

1:1.66 

114 

10.3 

45 

707 

10.9 

14.3 

1,364 

1:1.93 

123 

11.1 

32 

30 

804 

13.3 

9. .'. 

834 

1:1.03 

79 

10.  5 

35 

804 

12.8 

11.1 

1,067 

1:1.32 

100 

10.7 

40 

804 

12.4 

12.7 

1,305 

1:1.02 

114 

11.4 

45 

804 

11.9 

14.3 

1,527 

1:1.90 

123 

12.4 

50 

804 

11.5 

15.9 

1, 750 

1:2.17 

129 

13.6 

34 

30 

908 

14.3 

9.5 

906 

1:1.00 

70 

4.9 

35 

908  i 

13.8 

11.1 

1, 161 

1:1.28 

95 

12.0 

40 

908 

13.4 

12.7 

1,433 

1:1.58 

112 

12.8 

45 

908 

12.9 

14.3 

1,684 

1:1.85 

121 

13.  9 

50 

908 

12.  5 

15.9 

1,951 

1:2.14 

128 

L5.2 

36 

35 

1,018 

14.8 

11.1 

1,265 

1:1.24 

95 

13.3 

40 

1,018 

14.4 

12.7 

1,560 

1:1.53 

110 

14.2 

45 

1,018 

13.9 

14.3 

1,844 

1:1.  SI 

120 

15.3 

50 

1,018 

13.4 

15.  9 

2.149 

1:2.11 

128 

10.  7 

55 

1,018 

13.0 

17.5 

2,428 

1:2.38 

132 

18.4 

38 

35 

1,134 

15.8 

11.1 

1,360 

1:1.20 

93 

14.6 

40 

1.134 

15.4 

12.7 

1,688 

1:1.48 

107 

15.7 

4:. 

1,134 

14.9 

14.3 

2,005 

1:1.76 

118 

17.0 

50 

1,134 

14.4 

15.9 

2.348 

1:2.07 

126 

18.7 

55 

1.134 

14.0 

17.5 

2  668 

1:2.35 

132 

20.2 

40 

40 

1,256 

16.4 

12.7 

1,816 

1:1.44 

106 

17.0 

45 

1,256 

15.9 

14.3 

2.  165 

1:1.72 

117 

18.5 

50 

1,256 

15.  4 

15.9 

2. 540 

1:2.02 

125 

20.  3 

55 

1,256 

15.0 

17.5 

2,909 

1:2.31 

131 

60 

1,256 

14.5 

19.1 

3.25(1 

1:2.59 

135 

24.1 

42 

40 

1 .  385 

17.4 

1_\  7 

1,943 

1:1.40 

105 

18.5 

45 

1 .  385 

16.9 

14.3 

2,326 

1:1.68 

115 

20.2 

50 

1.385 

16.4 

15.9 

2.  745 

1:1.98 

124 

22.  1 

55 

1 .  385 

16.0 

17.5 

3.149 

1:2.27 

130 

24.2 

60 

1,385 

15.5 

19.1 

3,542 

1:2.55 

135 

26.2 

44 

45 

1.520 

17.9 

14.3 

_'.  186 

1:1.03 

114 

21.8 

50 

1,520 

17.4 

15.9 

2.944 

1:1.93 

123 

23.9 

55 

1.520 

17.0 

17.5 

3,389 

1:2.22 

130 

26.1 

60 

1.520 

16.5 

19.1 

1:2.52 

135 

28.3 

65 

1,520 

16.1 

20.7 

4. 254 

1:2.80 

138 

30.8. 

49918— Bull.  76 — 08 4 


48 


FUMIGATION    FOR    THE    CITRUS    WHITE    FLY. 


Table   IX.—  Recommended  dosage ,  with  -io-minute  exposures — Continued. 


Measurements  of 

Height 

Diameter 

Rate  of 

tented  tie 

of  regular 

of  regular 

Ratio  of 

dosage, 

Amount 
of  cyanid 

Area  of 

figure 

figure 

leakage 

number 

leakage 

with 

with 

Volume. 

surface 

cubic  feet 

Distance, 
over. 

Circum- 
ference. 

surface. 

foregoing 
measure- 
ments. 

foregoing 
measure- 
ments. 

to  cu  bit- 
contents. 

space  per 
ounce 
cyanid. 

recom- 
mended. 

Feet. 

Feet. 

Sq.  feet. 

Feet. 

Feet. 

Cu.feet. 

Ounces. 

46 

50 

1,662 

18.4 

15.9 

3.133 

1:1.88 

121 

25.9 

55 

1,662 

17.9 

17.5 

3.630 

1:2.18 

129 

28.1 

60 

1,662 

17.5 

19.1 

4,115 

1:2.47 

134 

30.7 

65 

1,662 

17.0 

20.7 

4,591 

1:2.76 

138 

33.2 

70 

1,662 

16.6 

22.3 

5,038 

1:3.03 

141 

3.5.7 

48 

50 

1.810 

19.4 

15.9 

3.332 

1:1.84 

121 

27.  5 

55 

1,810 

18.9 

17.5 

3,870 

1:2.13 

128 

30.  2 

60 

1.810 

18.5 

19.1 

4.401 

1:2.43 

133 

33.  1 

65 

1.810 

18.0 

20.7 

4,927 

1:2.72 

137 

&5.9 

70 

1,810 

17.6 

22.3 

5,428 

1:3.00 

141 

38.5 

50 

55 

1,964 

19.9 

17.5 

4,111 

1:2.09 

127 

32.4 

60 

1.904 

19.5 

19.1 

4,687 

1:2.38 

132 

35.5 

65 

1.964 

19.0 

20.7 

5,264 

1:2.63 

136 

38.7 

70 

1,964 

18.6 

22.3 

5,828 

1:2.96 

140 

41.6 

75 

1.964 

18.2 

23.9 

6,358 

1:3.24 

142 

44.7 

52 

55 

2,123 

20.9 

17.5 

4,351 

1:2.05 

126 

34.  5 

60 

2.  123 

20.5 

19.1 

4.974 

1:2.34 

132 

37.6 

65 

2.123 

20.0 

20.7 

.5.  600 

1:2.63 

136 

41.1 

70 

2.123 

19.6 

22.3 

6. 217 

1:2.92 

140 

44.4 

75 

2.123 

19.2 

23.9 

6.805 

1:3.20 

142 

47.9 

54 

55 

2,289 

21.9 

17.5 

4.  .591 

1:2.00 

125 

36.7 

60 

2,289 

21.5 

19.1 

5,261 

1:2.30 

131 

40.1 

65 

2.2S9 

21.0 

20.7 

5,936 

1:2.60 

136 

43.6 

70 

2.289 

20.6 

22.3 

6,607 

1:2.88 

138 

47.8 

75 

2,289 

20.2 

23.9 

7.252 

1:3.16 

142 

51.1 

56 

60 

2.462 

22. ."» 

19.1 

.5.  .547 

1:2.25 

130 

42.6 

65 

2,462 

22.0 

20.7 

6.273 

1:2.54 

135 

46.4 

70 

2,462 

21.6 

22.3 

6,997 

1:2.84 

138 

50.7 

75 

2,462 

21.2 

23.9 

7.700 

1:3.12 

142 

54.2 

80 

2,462 

20.8 

25.5 

8,459 

1:3.43 

144 

58.7 

58 

60 

2.641 

23.5 

19.1 

5,834 

1:2.20 

130 

44.8 

65 

2.641 

23.0 

20.7 

6,609 

1:2.50 

135 

48.8 

70 

2.641 

22.6 

22.3 

7.396 

1:2.80 

138 

53.6 

75 

2,641 

22.2 

23.9 

8,147 

1:3.09 

141 

57.7 

80 

2,641 

21.8 

25.  5 

8,971 

1:3.39 

144 

62.3 

60 

60 

2,826 

24.5 

19.1 

6,120 

1:2.16 

128 

47.8 

65 

2.826 

24.0 

20.7 

6.945 

1:2.45 

134 

51.8 

70 

2.826 

23.6 

22.3 

7,786 

1:2.75 

138 

56.4 

75 

2.826 

23.2 

23.9 

8.595 

1:3.04 

141 

60.9 

80 

2.826 

22.8 

25.5 

9,483 

1:3.35 

144 

65.4 

62 

60 

3.018 

25.5 

19.1 

6.  406 

1:2.12 

128 

50.0 

65 

3,018 

25.0 

20.7 

7,282 

1:2.41 

133 

54.  7 

70 

3,018 

24.6 

22.3  • 

8,176 

1:2.71 

137 

59.6 

75 

3.018 

24.2 

23.9 

9.042 

1:3.00 

141 

64.1 

80 

3,018 

23.8 

2.5.  .5 

9. 99.5 

1:3.31 

143 

69.2 

64 

60 

3. 215 

26.5 

19.1 

6.693 

1:2.08 

126 

53.1 

65 

3.215 

26.  C 

20.7 

7. ..is 

1:2.37 

132 

57.  7 

70 

3.  215 

25.6 

22.3 

8,565 

1:2.66 

136 

63.0 

75 

3. 215 

25.2 

239 

9.489 

1:2.95 

140 

67.7 

80 

3.  215 

24.8 

25.  .5 

10.507 

1:3.26 

143 

73.4 

66 

60 

3.419 

27.  5 

19.1 

6.979 

1:2.04 

126 

5.5.  4 

65 

3.419 

27.0 

20.7 

7. 955 

1:2.33 

131 

60.7 

70 

3.419 

26.6 

22.3 

8.955 

1:2.61 

134 

66.8 

75 

3.  419 

26.2 

23.9 

9.937 

1:2.90 

140 

70.9 

80 

3.419 

25.8 

25.5 

11.019 

1:3.22 

142 

77.  6 

85 

3.419 

25.3 

27.1 

11,939 

1:3.49 

144 

82.9 

68 

60 

3.630 

28.5 

19.1 

7. 266 

1:2.00 

125 

58.1 

65 

3.630 

28.0 

20.  7 

8.290 

1:2.28 

130 

63.7 

70 

3,630 

27.6 

22.3 

9.  345 

1:2.57 

135 

69.  2 

75 

3.630 

27.2 

23.9 

10. 384 

1:2.86 

139 

74.6 

80 

3.630 

26.8 

25.5 

11.531 

1:3.17 

142 

81.1 

85 

3.630 

26.3 

27.1 

12.513 

1:3.45 

144 

87.5 

70 

60 

3,848 

29.5 

19.1 

7,552 

1:1.96 

123 

61.4 

65 

3.848 

29.0 

20.7 

.  8.  627 

1:2.24 

130 

66.3 

70 

3,848 

28.6 

22.3 

9.734 

1:2.53 

135 

72.1 

75 

3.848 

28.2 

23.9 

10.S31 

1:2.81 

138 

78.5 

80 

3.848 

27.8 

25.5 

12.  043 

1:3.10 

142 

84.8 

85 

3.848 

27.3 

27.1 

13.088 

1:3.40 

144 

90.9 

72 

60 

4.069 

30.5 

19.1 

7.838 

1:1.92 

123 

63.7 

65 

4.069 

30.0 

20.7 

8.963 

1:2.20 

130 

68.9 

70 

4.069 

29.6 

22.3 

10. 124 

1:2.49 

134 

75.  5 

75 

4.069 

29.2 

23.9 

11.278 

1:2.77 

137 

82.3 

80 

4.069 

28.8 

25.5 

12.  555 

1:3.08 

141 

89.0 

85 

4.069 

28.3 

27.0 

13.662 

1:3.35 

144 

94.8 

90 

4,069 

27.8 

28.6 

14.829 

1:3.04 

146 

101.5 

D08AG]     REQ1  1KI..M  i  N  r8. 


I'.i 


X  \i.i  1    1  v     Re*  ommendtd  dotage,  u  Uh 

inued. 

Diameter 

1 

of  n-pilar 

cubic  i'-«'t 

space]  er 

ounce 

with 
measure 

li).'iin- 

Ulth 

Volume. 

1..  (Mil, If 
COllt«'Ilt- 

Circiini 

mended. 

111.  ills. 

mente. 

(„.    /,,/. 

oyanid. 

1  ,■■ 

71 

.,<) 

81.5 

[ft  1 

v  L2S 

1:1.  y» 

121 

.,7  1 

8L0 

20.7 

9,300 

1:2.  is 

129 

71.3 

70 

80.  (i 

10,513 

1:2.46 

184 

7-    1 

77. 

aa  2 

11,726 

1:2.72 

187 

90 

25. :, 

13,067 

1:3.03 

Ml 

6 

29.  3 

27.0 

14,237 

1:8.81 

148 

'.XI 

28.6 

15,  171 

i:aeo 

11., 

106.0 

76 

1.. 

32.  r, 

19  1 

8,411 

1:1.85 

120 

70.0 

86 

32  0 

-'n.7 

9,635 

1:2.  12 

128 

75.  2 

7'i 

81.6 

22.  3 

10,903 

1:2.  in 

133 

7-, 

3L2 

28.  g 

12.  173 

136 

Ml 

At),  s 

25.  ■". 

\:i.:,:\i 

1:2.99 

110 

!f7.() 

V, 

sa  a 

27.0 

14,812 

1:3.28 

148 

1(13.:, 

90 

29.8 

28.6 

hi.  113 

1   3.55 

145 

111.  1 

EXPERIMENTS    WITH    BELL   OR    HOOP   TENT. 

The  boll  or  hoop  tent  used  in  these  experiments  was  one  constructed 
of  6J-ounce  drill  of  the  brand  most  commonly  used  in  California. 
Owing  to  the  form  of  the  tent  the  leakage  surface  is  far  less  in  propor- 
tion to  the  volume  than  in  the  sheet  tent.  The  data  concerning  the 
experiments  and  the  recommended  dosage  based  upon  the  experi- 
ments with  the  sheet  tent  are  given  in  Table  X. 

Table  X. — Experiments  in  fumigation  with  bell-shaped  tent  of  6\-ounce  drill. 


Measurements  of 

Amount  of 

Ex- 

tented trees. 

Number  of 

cyanid 

Amount  of 

white 

Per  cent  of 

recom- 

peri- 
ment 
No. 

cyanid 

flies  un- 

white flies 

mended  in 

Distance 

Circumfer- 

used. 

der  obser- 

killed. 

table  for 

over. 

ence. 

vation. 

45  minutes' 

exposure. 

Feet. 

Feet. 

Ounces. 

Ounces. 

30.3 

28* 

35 

4 

555 

88 

9 

40.5 

27 

38 

4 

138 

88 

8* 

40.7 

33* 

38 

8* 

132 

80 

13 

40.16 

20 

23 

4 

300 

100 

4* 

40.17 

25* 

27 

7 

476 

100 

7 

40.19 

24 

20 

4 

209 

100 

51 

40.22 

20 

22 

2 

162 

97.4 

4 

47,.  2 

28 

29 

7 

427 

100 

8* 

45.11 

2ti 

31* 

| 

284 

100 

7* 

45.14 

31 

35 

289 

100 

104 

45.  Hi 

27* 

29 

6J 

431 

100 

8* 

45.18 

27 

34.'. 

9i 

.v.).-, 

100 

8 

4:,.  2'.' 

29* 

30 

6 

530 

10(1 

••'. 

45.31 

23 

24 

31 

376 

98.7 

6 

50.3 

24* 

31* 

4 

128 

97.  6 

7 

50.4 

34* 

37" 

51 

990 

100 

14 

60.8 

26 

31 

42 

85.7 

71 

X.2 

33 

35 

11 

200 

100 

12* 

In  these  experiments  a  dosage  sufficient  to  destroy  all  pupa3  was 
used  in  eleven  instances.  The  total  amount  of  cyanid  used  in  the 
eleven  experiments  was  78J  ounces,  whereas  the  doses  recommended 
in  the  tables,  based  upon  the  experiments  with  the  sheet  tents  of 
8-ounce  duck,  together  amounted  to  96  ounces.  The  average  of  the 
amounts  used  in  the  eleven  tests  was  7.2  as  against  8.7  recommended 


50  FUMIGATION    FOR   THE   CITRUS    WHITE   FLY. 

in  the  tables.  It  is  evident  from  the  results  summarized  in  the  fore- 
going table  that  prolongation  of  the  period  of  exposure  beyond  40 
minutes  produces  no  noticeable  increase  in  effectiveness.  It  is  also 
evident  that  the  dosage  recommended  for  use  with  sheet  tents  of 
a  good  quality  of  8-ounce  duck  is  ample  for  bell  tents  of  a  good  quality 
of  6J-ounce  drill.  The  smaller  amount  of  leakage  surface  with  bell 
tents  as  compared  with  sheet  tents  may  be  entirely  responsible  for  the 
apparently  wide  margin  between  the  recommended  dosage  and  the 
dosage  actually  required  for  efficiency,  but  it  seems  safe  to  conclude 
that  the  6J-ounce  drill  used  in  the  bell  tent  held  the  gas  approxi- 
mately as  well  as  the  8-ounce  duck,  the  difference  in  leakage  surface 
considered. 

MISCELLANEOUS  EXPERIMENTS  AND  OBSERVATIONS. 

APPEARANCE    OF    LARVAE    AND    PUP.E    OF    THE    WHITE    FLY    WHEN    DE- 
STROYED   BY   FUMIGATION. 

The  opportunities  for  studying  the  efficiency  of  the  gas  against 
citrus  pests  are  far  superior  with  the  white  fly  as  compared  with 
the  true  scale  insects.  While  it  requires  considerable  skill  in  the 
examinations,  the  vital  conditions  of  the  larvae  and  pupa?,  both 
before  and  after  treatment,  can  be  recognized  with  practical  cer- 
tainty without  removing  the  specimens  from  the  leaves.  When  in  a 
normal  condition  the  insects  in  the  stages  mentioned  appear  green, 
owing  to  their  translucence,  and  paired  yellowish  spots,  due  to  inter- 
nal organs,  are  sometimes  visible  in  the  abdominal  region.  As  the 
pupa  reaches  maturity  the  reddish  eyes  of  the  adult  become  conspicuous 
and  the  location  of  the  developing  adult  wings  is  indicated  by  whitish 
patches  on  either  side  of  the  body.  When  destroyed  by  fumigation 
with  hydrocyanic-acid  gas  the  larva?  and  pupa?  usually  turn  more  or 
less  brownish  in  the  course  of  a  few  days.  This  brownish  discolora- 
tion is  most  pronounced  along  the  middle  of  the  body.  Frequently, 
however,  two  or  three  weeks  may  elapse  before  they  can  be  positively 
determined  as  dead.  In  the  first  examinations  made  by  the  author, 
pupa?  on  fumigated  trees  were  classed  as  alive,  doubtful,  and  dead. 
It  was  afterwards  determined  that  in  practically  every  case  those 
classed  as  doubtful  were  in  reality  dead.  Examinations  under  a 
compound  microscope  were  found  to  be  of  some  assistance  at  times, 
but  on  the  whole  unsatisfactory.  In  such  cases  movements  of  the 
internal  organs  furnish  positive  proof  that  the  insect  is  alive,  but 
when  these  movements  can  not  be  detected  there  may  still  be  doubt 
concerning  the  condition  of  the  specimen  unless  granulation  or  dis- 
coloration of  the  body  contents  is  evident.  The  most  satisfactory 
method  of  observing  the  results  of  fumigation  is  to  examine  the 
insects  with  a  hand  lens  of  1  or  1 J  inch  focal  distance  without  dis- 


\  III   \l;  \\«  I     0]     l   \KV  .!■:    \ND    ITI'i;    WHEN     UES'I  \:><\  I  D. 


51 


burbing  the  insect  <>r  detaching  the  leal  From  the  tree.  String 
attached  to  leaves  upon  which  are  specimens  classed  us  doubtful 
will  enable  examinations  of  such  specimens  from  time  to  time  until 
their  condition  is  positively  determined.  A  careful  examination  of 
normal  specimens  and  direct  comparisons  of  these  with  those  on 
leaves  of  fumigated  trees  will  assist  in  the  ready  identification  of  the 
dead  insects. 

DENSITY     OF    THE    GAS    AT    VARIOUS    HEIGHTS    ABOVE    THE    GROUND. 

It  is  natural  to  presume  that  owing  to  the  fact  that  hydrocyanic- 
acid  gas  is  lighter  than  air,  its  density  during  the  process  of  fumiga- 
tion is  greater  toward  the  top  of  the  tree.  In  four  of  the  nine  obser- 
vations on  the  comparative  effect  of  the  gas  at  different  heights 
above  ground  the  results  of  this  variation  in  density  are  not  evident. 
In  the  other  five  observations  the  results  are  quite  striking.  In  the 
six  experiments  in  which  observations  were  made  10  feet  or  more 
from  the  ground,  the  average  percentage  of  insects  killed  up  to  6 
feet  above  the  ground  was  64,  while  from  10  to  18  feet  above  ground 
the  average  percentage  killed  was  71.  The  data  concerning  the 
ell'cctiveness  of  the  gas  at  various  distances  from  the  ground  is  sum- 
marized in  Table  XI. 

Table  XI. — Efficiency  of  gas  as  affected  by  height  above  ground. 


Ex- 
peri- 

Distance 
above 
ground. 

Number  of 
white  fly 

Per  cent 

Ex- 
peri- 

Distance 

Number  of 
white  fly 

Per  cent 

ment 
No. 

pupae  ex- 
amined. 

killed. 

ment 
No. 

ground. 

pupae  ex- 
amined. 

killed. 

Ft  1 1. 

Feet. 

30.4 

4-0 

427 

89 

30.1 

4-6 

74 

21 

14-15 

244 

98.3 

12-14 

909 

3b 

18 

120 

100 

40.3 

4-6 

822 

80 

20.1 

4-6 

687 

91.9 

12-14 

445 

90.8 

12-14 

1,000 

90.8 

30.3 

2 

396 

92.8 

20.7 

4-5* 

222 

77 

3i-7 

159 

78 

10 

306 

60 

40.7 

2 

93 

80.6 

40.12 

2 
3J-5 
4-6 
14-16 

112 

728 
541 
136 

64 
98.4 
26.4 
50 

4-6 

139 

79.2 

The  results  show  that  when  examining  for  the  results  of  fumigation, 
the  most  significant  effects  are  those  within  a  few  feet  of  the  ground. 
The  observations  concerning  the  results  of  the  experiments  upon 
which  the  recommendations  in  this  bulletin  are  based  were  made  in 
all  cases  within  7  feet  of  the  ground,  and  included  examinations  of 
insects  on  leaves  closest  to  the  ground  in  all  cases. 


EFFECT  OF  FUMIGATION  ON  THE  TREES. 

During  the  months  of  December,  January,  and  February,  until  the 
appearance  of  the  new  spring  growth,  fumigation  for  the  white  fly 
with  the  dosage  herein  recommended  will  rarely  occasion  appreciable 


52  FUMIGATION    FOR   THE   CITRUS   WHITE   FLY. 

injury  to  orange  trees  and  apparently  never  to  tangerine  and  grape- 
fruit trees.  The  liability  of  injuring  trees  through  the  emptying  of  the 
contents  of  the  jars  after  fumigation  close  to  or  upon  the  base  of  the 
trees  will  be  referred  to  under  the  subject  of  precautions.  The  injury 
to  orange  trees  from  the  gas  itself  has  never  in  the  writer's  experience 
been  sufficient  to  offset  the  benefits  of  destroying  the  white  fly  and 
scale  insect  pests.  Nevertheless  the  subject  is  one  of  considerable 
importance.  The  experiments  conducted  in  January  and  February, 
1907,  demonstrated  the  practicability  of  destroying  the  white  fly 
with  hydrocyanic-acid  gas  without  injury  to  citrus  trees. 

The  fumigation  of  nearly  4,000  trees  in  the  winter  of  1907-8  has 
greatly  extended  our  knowledge  of  the  effect  of  fumigation  upon  the 
trees,  but  there  remain  several  unsolved  problems  in  this  connection 
which  it  is  hoped  will  be  elucidated  by  future  experience.  The  work 
of  fumigating  a  grove  should  be  completed  if  possible  before  the  new 
growth  appears  in  the  spring.  Under  certain  temperature  conditions 
successful  fumigations  may  occasion  no  injury  to  new  growth,  but 
there  is  danger  of  destroying  the  first  spring  shoots  which  normally 
produce  the  greater  part  of  the  blooms.  When  affected  by  the  gas 
new  shoots  wilt  and  turn  dark,  appearing  as  though  affected  by  frost. 

Under  certain  conditions  there  is  more  or  less  shedding  of  the  old 
leaves  following  fumigation.  The  loss  of  10  or  15  per  cent  of  the  old 
foliage  can  not  be  considered  an  injury,  inasmuch  as  even  more  than 
this  proportion  is  usually  shed  during  the  winter  or  in  the  spring.  In 
fact,  it  has  been  demonstrated  by  experiments  conducted  by  Mr. 
Yothers  and  the  writer  in  February,  1908,  that  the  leaves  shed  by 
fumigation  when  the  percentage  of  the  whole  does  not  exceed  15  per 
cent  are  among  the  leaves  which  would  normally  drop  in  the  course 
of  a  few  weeks. 

In  the  experiments  with  the  sheet  tent  of  8-ounce  duck  summarized 
in  Table  IV,  the  most  extensive  shedding  occurred  in  experiments 
40.14.  In  this  it  was  estimated  that  about  50  per  cent  of  the  leaves 
were  shed.  The  tree  was  fumigated  on  January  29,  beginning  at 
4.07  p.  m.,  about  one-half  hour  before  sunset.  No  shedding  was 
observed  until  the  morning  of  February  2,  when  it  was  estimated  that 
from  15  to  20  per  cent  of  the  leaves  dropped.  On  February  4  it  was' 
estimated  that  50  per  cent  of  the  leaves  had  fallen,  after  which  date 
the  amount  of  the  shedding  was  inappreciable.  The  winged  petioles 
of  the  leaves  remained  attached  to  the  tree  in  most  cases  and  the 
fallen  leaf  blades  showed  distinct  brownish  areas  due  to  burning  by 
the  gas.  The  tree  consisted  of  five  stems  growing  from  the  roots  of  a 
tree  frozen  to  the  ground  in  1895.  One  of  these  stems  was  affected 
by  foot  rot  or  mal-di-gomma,  and  the  defoliation  of  this  was  nearly 
complete,  materially  increasing  the  percentage  of  shedding  from  the 


I  I  I  1 1<    l     01      li    VI 10  ATI  ON    ON     II:  I 

tree  as  a  whole.  This  tree  was  observed  in  full  !>l<>.>in  on  April  I.  and 
ten  months  after  the  treatment  appeared  as  \iLr<>i"u-  as  ;m\  tree  in 
the  grove  and  bore  more  than  the  average  crop  of  fruit.  In  1 1 1<* 
experiments  with  the  l><'ll  tent  of  6J-ounce  drill,  shedding  of  conse 
quence  occurred  only  in  the  case  of  experiment  X.J.  This  tree  was 
fumigated  on  January  29,  beginning  ai  1. 1 1  and  ending  at  7.50  p.  m. 
It  was  estimated  that  the  shedding  amounted  t<>  about  •'!<>  per  cent 
in  this  case. 

In  experiment  45.36  the  exposure  began  at  .'!.(>7  p.  m.in  bright  sun- 
light with  the  temperature  at  75°  F.  The  lent  had  been  in  position 
for  thirty  minutes  preceding  the  introduction  of  the  chemicals,  and 
the  inside  temperature  was  \\°  higher  at  the  beginning  than  the  out- 
side temperature  mentioned  above.  The  tent  was  in  direct  sunlight 
during  the  entire  forty-live  minutes  of  exposure,  and  doubtless  the 
inside  temperature  rose  to  82°  or  83°.  As  shown  in  Table  IV .  the 
amount  of  potassium  cyanid  used  was  41  ounces  less  than  the 
amount  recommended  in  the  table  given  in  tlie  appendix.  The 
Leaves  were  curled  as  a  result  of  drought  at  the  time  of  the  fumiga- 
tion and  no  shedding  of  leaves  or  injury  of  any  kind  to  the  tree  could 
be  detected  by  subsequent  examinations. 

An  overdose  is  indicated  by  the  scorching  of  the  foliage  on  entire 
twigs.  This  is  more  likely  to  occur  near  the  tops  of  the  trees.  In 
such  cases  several  twigs,  each  6  inches  or  a  foot  in  length,  may  be 
entirely  killed,  the  leaves,  instead  of  dropping  within  a  few  days, 
turning  brown  and  remaining  attached  to  the  dead  twig.  This  is 
not  necessarily  accompanied  by  excessive  shedding  of  the  foliage. 
The  physiological  condition  of  the  trees  seems  to  have  a  marked 
effect  on  their  liability  to  shed  foliage.  Vigorous  trees  are  less 
susceptible  than  weak,  poorly  nourished  ones.  Trees  in  the  same 
grove  but  growing  under  different  conditions  as  regards  the  nature 
of  the  soil  and  the  amount  of  soil  moisture  show  differences  in  this 
respect.  In  most  groves  trees  will  not  shed  leaves  excessively  if 
the  dosage  is  increased  25  per  cent  above  the  recommended  amount-. 
Frequently  there  will  be  no  shedding  at  all  following  such  a  course. 
In  other  citrus  groves  the  recommended  dose  is  as  large  as  the  trees 
will  stand  without  shedding  to  an  injurious  extent. 

The  likelihood  of  damaging  citrus  fruits  by  fumigation  is  such  that 
it  is  strongly  advisable  to  pick  the  crop  before  starting  to  fumigate. 
In  January,  1908,  many  seedling  trees  were  fumigated  which  held 
from  five  to  eight  boxes  of  oranges  per  tree,  without  any  injury 
whatever  following  the  treatment.  In  other  cases  a  small  percent- 
age of  the  fruit  developed  sunken  areas  or  "pits"  which  turned  dark 
and  ruined  the  affected  fruit  for  shipping  purposes.  Fumigation 
in  midwinter,  using  the  dosage  t able  given  in  the  appendix,  does  not 
seem  to  affect  the  fruit  of  Hart's  Lake,  Lamb's  Summer,  or  Valencia 


54  PUMIGATIOU    FOR    THE   CITRUS   WHITE  FLY. 

varieties.  Grapefruits  arc  slightly  susceptible  to  this  injury,  while 
tangerines  appear  not  at  all  susceptible,  although  considerable  shed- 
ding of  the  fruit  occurred  in  one  instance  when  the  recommended 
dosage  was  doubled. 

SUGGESTIONS  FOR  THE   FUMIGATION  OF  SMALL  TREES. 
IX    THE    GROVE. 

In  discussing  the  style  of  fumigating  tents  desirable  for  use  against 
the  white  fly  the  author  has  referred  to  the  advantages  of  the  use  of 
box  covers  for  small  trees.  In  many  cases  complete  defoliation  of 
the  trees  during  the  winter  months  would  be  the  best  method  of 
checking  the  pest,  but  fumigation  is  preferable  under  most  circum- 
stances. The  dosage  with  box  covers  will  depend  upon  the  tightness 
of  the  cloth  used.  It  has  been  recommended  that  the  cloth  be  made 
as  nearly  air-tight  as  possible  by  means  of  paint,  or  that  air-tight 
oilcloth  be  used.  The  rate  of  dosage  can  be  readily  determined  by 
means  of  a  series  of  tests,  beginning  with  1  ounce  of  potassium 
cyanid  for  each  170  cubic  feet  of  space  (0.00588  ounce  per  cubic 
foot)  and  decreasing  the  number  of  cubic  feet  per  ounce  10  feet  for 
each  experiment  until  the  results  are  satisfactory  and  uniform.  Xo 
experiments  have  thus  far  been  conducted  by  the  author  along  these 
lines,  but  it  is  expected  that  in  the  course  of  the  investigations  of 
the  white  fly  now  under  way  in  Florida  this  phase  of  white  fly  con- 
trol will  be  given  consideration. 

IX    THE    XURSERY. 

Several  square  yards,  including  many  trees,  can  be  covered  in  the 
nursery  by  a  single  tent.  If  the  cloth  is  unpainted,  the  dosage  for  a 
first  trial  can  be  calculated  by  first  determining  the  ratio  of  the  leak- 
age surface  to  the  cubic  contents  and  referring  to  Table  VIII  in  this 
bulletin,  where  the  recommended  rate  of  dosage  will  be  found  for  the 
various  ratios.  The  results  of  the  preliminary  tests  should  be  care- 
fullv  observed  before  fumigating  on  a  large  scale,  in  order  that  the 
rate  of  dosage  may  be  adjusted  to  suit  the  tightness  of  the  cloth  used 
as  a  cover. 

XURSERY    STOCK    FOR    SHIPMEXT. 

Prof.  H.  A.  Gossard,  formerly  of  the  Florida  experiment  station, 
has  determined  that  in  an  air-tight  fumigatorium  1  ounce  of  potas- 
sium cyanid  for  each  170  cubic  feet  of  space  a  is  sufficient  to  destroy  all 

a  "One  gram  to  6  cubic  feet  of  space,"  he  reports,  "seemed  sufficient  to  kill  every- 
thing, but  to  make  the  dose  more  certain  1  gram  to  5|  cubic  feet  was  adopted  as  the 
standard  dose  and  has  been  repeatedly  tried,  always  giving  the  uniform  result  of  kill- 
ing all  larvae  (pupa?)  and  adults.'* — Bui.  67,  Fla.  Exp.  Sta.,  p.  652.  One  ounce  is 
equal  to  28.35  grams,  from  which  it  is  calculated  that  1  gram  for  6  cubic  feet  of  space 
is  equal  to  1  ounce  for  170  cubic  feet  and  1  gram  for  5|  cubic  feet  is  equal  to  1  ounce 
for  163  cubic  feet. 


Mi;.- 1  i:\    8T0<  K    FOB   SHIPMENT.  DO 

larvae  and  pupae  of  the  white  fly.  To  destroy  the  eggs,  however,  he 
found  that  a  larger  dose  was  necessary.  The  author  fully  concurs 
with  Professor  ( i<>^>anl  in  his  recommendation  to  defoliate  completely 
nil  white  il\  infested  nurserj  stock  before  shipping,  and.  ;i-  an  extra 
precaution,  t<>  fumigate.  The  almost  invariable  experience  of  Florida 
nurserymen,  however,  shows  that  citrus  trees  should  not  be  fumigated 
with  in.»t-  bare.  The  fumigation  is  far  less  necessary  than  when  tli<' 
insects  concerned  are  true  scale  insects  and  are  attached  to  tin'  Btems. 
White  flies  have  never  been  known  to  reach  maturity  except  on  the 
leaves,  although  eggs  and  crawling  larvae  may  occasionally  be  found 
on  young  growing  shoots.  It  is  safe  to  presume  that  there  arc  no 
unhatched  eggs  ^i'  the  white  fly  on  anything  other  than  leaves  and 
young  succulent  growth  of  stems.  When  these  are  completely  re- 
moved there  need  be  no  fear  that  the  pest  will  he  carried  by  means 
of  the  trees.  The  entire  leaves,  including  the  winged  leaf  petiole-. 
must  he  removed,  and  when  large  shipments  are  concerned  careful 
attention  must  he  given  to  this.  A  greater  danger  than  the  trees 
themselves  is  found  in  the  packing.  This,  as  Professor  Gossard 
points  out.  might  he  a  possible  source  of  danger  if  infested  citrus 
leaves  were  allowed  to  get  into  the  moss  or  other  material  used  in 
packing.  The  danger  is,  of  course,  slight,  but  should  nevertheless 
be  borne  in  mind  by  shippers  and  bivyers  of  nursery  stock. 

PRECAUTIONS. 

As  is  customary  in  publications  on  entomology  in  which  the  use  of 
potassium  cyanid  is  recommended  in  combating  insect  pests,  atten- 
tion is  directed  to  the  extremely  poisonous  nature  of  this  substance. 
There  are  on  record  no  fatalities  due  to  the  use  of  potassium  cyanid 
a-  an  insecticide  against  orchard  pests,  but  this  is  because  the  danger 
from  careless  use  was  well  known  and  simple  precautions  were 
observed.  In  weighing  the  doses  it  is  recommended  that  the  hands 
be  protected  by  leather  gloves,  and  after  starting  the  generation  of 
the  gas  the  operator  should  avoid  breathing  until  he  is  outside  in  the 
open  air.  A  slight  choking  sensation  experienced  when  standing 
close  to  the  tents  during  the  fumigation  acts  as  a  danger  signal,  and 
one  should  not  persist  in  remaining  where  the  gas  is  dense  enough  to 
produce  this  result.  The  acid  should  always  be  handled  with  great 
care.  In  addition  to  precautions  necessary  for  the  safety  of  the 
operators,  care  should  be  taken  to  avoid  the  scattering  of  small  parti- 
cles of  the  cyanid  where  fowls  or  other  animals  might  become  poisoned. 
As  this  substance  is  readily  soluble  in  water  and  is  deliquescent,  or 
capable  of  liquefying  through  the  absorption  of  moisture  from  the 
air,  small  particles  accidentally  dropped  soon  disappear. 


56 


FUMIGATION    FOR    THE    CITRUS    WHITE    FLY. 


Other  precautions  which  it  seems  desirable  to  emphasize  at  this 
time  concern  the  avoidance  of  damage  to  the  tents  and  trees.  Tents 
should  never  be  dragged  over  the  ground  where  the  residue  of  the 
jars  has  been  poured  out  on  the  surface  or  where  the  material  has 
boiled  over  during  the  generation  of  the  gas.  The  safest  rule  is  to 
avoid  entirely  the  dragging  of  tents  across  sections  of  the  grove 
which  have  been  recently  fumigated.  The  residue  or  contents  of  the 
jars  after  fumigating  is  very  destructive  to  citrus  trees  if  emptied 
against  the  base  of  the  trees.  When  emptied  3  feet  or  more  from 
the  base  of  the  trees  there  seems  to  be  no  danger  whatever  unless 
roots  are  exposed,  but  to  avoid  all  risk  it  is  recommended  that  the 
practice  be  adopted  of  burying  the  residue  halfway  between  the  rows, 
as  described  under  the  subject  of  methods  of  procedure.  Tents 
should  not  be  left  during  the  day  covering  trees  which  are  to  be 
fumigated  at  night,  for  the  inside  temperature  is  quite  likely  to  be 
raised  to  a  point  where  the  gas  will  cause  excessive  shedding  of  the 
foliage. 

EXPENSE  OF  FUMIGATION. 

FOR    EQUIPMENT. 


The  cost  of  the  equipment,  aside  from  the  fumigating  tents,  is  of 
little  importance.  In  procuring  a  set  of  tents  one  may  either  pur- 
chase the  material  and  arrange  for  the  construction  to  be  done  by  a 
tentmaker  according  to  directions,  or  the  maker  may  provide  the 
material  and  furnish  the  tents  according  to  specifications  at  regular 
prices.  It  will  be  found  advantageous  to  obtain  quotations  from  sev- 
eral tentmakers  before  placing  an  order.  To  give  an  idea  of  the 
usual  cost  of  fumigating  tents  in  California,  the  following  schedule 
of  prices  recently  quoted  by  a  leading  maker  of  fumigating  tents  in 
that  State  is  given: 

Table  XII. — Schedule  of  prices  for  sheet  and  bell  fumigating  tents. 


Sheet  tents,  8-ounce 

Bell  tents 

6^-ounce 

duck. 

drill. 

Diameter. 

Price. 

Dimensions. 

Price. 

Feet. 

Feet. 

17 

$6.12 

6bv    7 

$2.66 

24 

12.24 

8  by   9 

4.55 

30 

18.90 

6  by  12 

5.72 

36 

27.00 

9§  by  11 

6.76 

41 

34.20 

104  by  14 

9.10 

43 

41.40 

12  bv  15 

13.00 

45 

43.74 

48 

47.70 

52 

59.40 

55 

65.70 

64 

86.40 

C(.si    mi     EQUIPMENT,  .'.7 

The  cost  of  the  Bheet  tents  would  be  considerably  reduced  by  the 
use  of  one  or  two  widths  of  6J-ounce  drill,  sewed  around  the  margin 
as  b  skirt,  as  described  under  the  subject  of  construction  of  fumigat- 
ing tents.  The  difference  between  the  oo&1  of  tent  materials  in  Cali- 
fornis  and  in  eastern  citrus-growing  States,  owing  to  the  greater 
distance  of  the  former  from  the  factories,  should  resull  in  a  reduction 

of  from  2  to  5  per  cent    in  the  OOSf   of  an  outfit    at    any  point    in  the 

( hilf  States.     In  Florida  t  be  season  for  himigai  ing  against  i  lie  w  bite  fly 

extend-  over  from  seven  to  ten  week-.      During  this  t  ime  a  fumigat  mil: 

tent,  used  between  thirty-five  and  fifty  days  on  an  average  of  eight 
hours  per  day  with  forty-five  minute  exposures,  would  be  used  to 
cover  between  280  and  400  trees.     A  tent  large  enough  to  cover  the 

largest  trees  should  ordinarily  not  cost  over  SI  10.  It  has  been 
stated  that  the  tents  used  in  the  author's   experiments  in  January 

and  February,  1907,  have  not  deteriorated  appreciably.  With 
proper  care  tents  should  last  several  seasons,  whether  untreated 
or  mildew-proofed.  If  such  a  tent  as  referred  to  above  should  be 
used  for  only  three  seasons,  and  be  used  to  cover  only  between  280 
and  400  trees  each  season,  the  cost  of  the  wear  and  tear  of  the  tent 
would  amount  to  only  from  9  to  12  cents  per  tree.  Even  taking  into 
consideration  interest  on  the  money  invested,  the  cost  per  tree 
would  not  exceed  15  cents.  This  is  fully  twice  the  cost  of  a  tent 
large  enough  to  cover  trees  of  average  size. 

In  many  cases  it  would  not  be  advisable  for  an  orange  grower  to 
invest  several  hundred  dollars  in  fumigating  tents  for  his  exclusive 
use,  although  many  with  extensive  groves  would  doubtless  prefer 
to  do  this.  When  possible  individual  ownership  of  an  outfit  is  desir- 
able. In  some  citrus  fruit  growing  countries  where  fumigation  is 
practiced  against  scale  insects  several  growers  form  a  club  and 
share  the  cost  of  the  fumigating  outfit,  which  is  left  at  the  disposal 
of  each  of  the  members  in  turn.  Such  a  plan  might  be  followed  in 
many  cases  in  Florida.  It  is  especially  to  be  recommended  where 
several  groves  constitute  a  naturally  isolated  group,  and  cooperation 
has  all  the  advantages  of  individual  ownership  of  a  single  isolated 
grove.  A  few  citrus  growers  with  a  crop  worth  on  an  average  $25,000 
would  not  be  put  to  unreasonable  expense  in  the  joint  ownership  of 
an  outfit  costing  $1,200  or  $1,500.  The  rapid  growth  of  the  idea  of 
orange  growers'  associations  in  Florida  during  the  past  few  months 
leads  to  the  hope  that  a  means  is  at  hand  for  providing  for  systematic 
campaigns  against  citrus  pests.  In  some  cases  associations  for  this 
purpose  have  already  been  organized.  Fumigation  by  the  contract 
system,  as  it  is  now  done  to  a  large  extent  in  California,  may  also 
come  into  use  in  Florida.  The  plan  which  can  be  most  strongly  rec- 
ommended is  for  the  work  to  be  done  bv  the  various  counties.     Each 


58  FUMIGATION    FOR    THE   CITBTJS    WHITE   FEY. 

county  where  the  citrus-growing  interests  are  of  importance  should 
maintain  an  outfit  of  tents  large  enough  for  the  needs  of  the  orange 
growers  within  its  limits,  and  fumigation  should  be  done  at  cost 
under  the  direction  of  the  county  horticultural  commission. 

FOR    CHEMICALS. 

The  principal  item  of  expense  in  connection  with  fumigation  is  the 
potassium  cyanid.  Fumigation  was  considered  profitable  in  Cali- 
fornia when  this  was  sold  in  quantities  for  65  cents  per  pound.  At 
present  hi  lots  of  100  pounds  this  can  be  procured  for  about  30  cents 
per  pound,  while  in  ton  lots  the  cost  is  from  20  to  23  cents  per  pound 
in  Florida,  Sulphuric  acid  in  iron  drums  containing  about  1,500 
pounds  can  be  obtained  for  about  1^  cents  per  pound.  In  carboys 
containing  about  200  pounds  the  cost  is  about  2  cents  per  pound. 

FOR    LABOR. 

In  California,  labor  is  usually  paid  for  by  the  hour.  The  fore- 
man in  charge  of  the  outfit  is  generally  paid  about  40  cents  per  hour 
and  the  remainder  of  the  crew  about  25  cents  per  hour.  A  crew  of 
seven  men,  which  might  be  used  to  advantage  with  the  method  of 
procedure  herein  recommended  for  use  in  fumigating  for  the  white 
fly,  would  cost  $15.20  for  a  night's  work  of  eight  hours  if  wages  were 
paid  at  the  above  rates.  These  men  could  ordinarily  handle  from 
10  to  15  tents  of  the  largest  sizes  every  forty-five  minutes  and  fumi- 
gate 80  to  120.  trees  in  eight  or  nine  hours.  If  80  trees  were  treated, 
the  cost  for  labor  would  be  about  19  cents  per  tree.  If  smaller  tents 
were  used  and  handled  with  changing  poles,  the  same  crew  could 
treat  200  trees  in  eight  hours  at  a  cost  for  labor  averaging  about  7§ 
cents  per  tree.  If  six  men  proved  sufficient  to  do  this  work,  the  cost 
for  labor  would  be  about  1  cent  less  per  tree.  In  California  contract- 
ors charge  from  4  to  12  cents  per  tree  for  covering  trees  which  can  be 
covered  without  the  use  of  the  braced  uprights  or  derricks.  These 
prices  include  from  the  contractor's  standpoint:  First,  cost  of  labor; 
second,  cost  of  wear  and  tear  on  tents;  third,  a  reasonable  profit. 
Contractor's  prices  stated  above  are  exclusive  of  about  3  or  Sh  cents 
per  pound  usually  allowed  as  payment  for  handling  the  cyanid,  the 
chemicals  being  furnished  by  the  owner  of  the  grove. 

In  estimating  the  expense  for  labor  in  fumigating  a  grove  there 
should  be  included,  in  addition  to  the  labor  in  connection  with  cover- 
ering  the  trees  and  generating  the  gas,  an  allowance  for  repairing 
tents,  hauling  chemicals  and  water,  and  miscellaneous  work.  This 
ordinarily  ranges  from  1  to  4  cents  per  tree,  according  to  size. 


LOSS1  S    I  K(  'M     W  II  I  I  I      KM     ri;i.\  I.N  I  I  l». 


ECONOMY  OF  TREATMENT  BY   FUMIGATION. 


LOSSES    PREVENTED. 


Fig. 8.— Whitefly  (Aleyrodescilri):  a,  Orange  leaf,  show* 
ing  infestation  on  under  surface,  natural  size;  b,  egg; 

«  ,  same,  with  young  insect  emerging;  d,  larval  insect; 
e,  foot  of  same;  /,  larval  antenna;  g,  scale  like  pupa; 
h,  pupa  about  to  disclose  adult  insect ;  i .  insect  escap- 
ing from  pupal  shell;  /'.  leg  of  newly  emerged  insect, 
not  yet  straightened  and  hardened.  All  figures  ex- 
cept a  greatly  enlarged  (reengraved  from  Riley  and 
Howard). 


1j>ss,s  from  tin  ir/iih  ihj.  When  once  the  white  ll\  (figs.  8,9 
reduced  to  an  inconsiderable  quantity  in  a  grove,  much  benefit  will 
result  from  careful  inspec- 
tions and  fumigations  of  sin- 
gle trees,  or  groups  of  trees, 
from  time  to  time  wherever 
the  insects  are  found  to  be 
multipl)  ing.  Thisv*  illgreatly 
delay  the  time  when  the  mul- 
tiplication of  the  insects  shall 
have  made  a  general  treat- 
ment again  necessary.  This 
practice  is  followed  in  Califor- 
nia in  the  control  of  various 
scales.  In  well-cared-for 
groves,  or  where  the  county 
horticultural  commissioners 
require  it,  scales  are  kept  in 
complete  subjection  by  fumi- 
gation and  the  appearance  of 
only  a  few  live  scales  on  a  tree  is  considered  a  reason  for  fumigating 
it  and  perhaps,  also,  surrounding  trees  as  well,  although  these  may 
appear  entirely  free  from  the  pest.  The  best 'results  from  fumiga- 
tion are  obtained  when  once  the 
various  pests  are  brought  under 
control  by  continuing  the  prac- 
tice as  a  preventive  rather  than 
as  a  remedy.  In  other  words, 
when  conditions  for  successful 
fumigation  for  the  white  fly  are 
favorable  or  after  they  have 
been  made  so,a  fumigation  can 
be  practiced  with  such  success 

Fig.  9.-White  fly  (Aleyrodes  cilriy.a,  Winged  male  that  a11   damage  from    the  white 

insect,  with  enlarged  view  of  terminal  segments  fly  will  be  obviated.     Y\  hell  once 

at  b:  c,  dorsal  view  of  winged  female,  with  enlarge-  .1  .  .         1  i  ,  , 

mentsof  ovipositor,  head,  antenna,  wing  margin.  the  practice  has  been  adopted  a 

and  leg  at  d,  e,f,  g,  h,i.    (Reduced  from  Riley  and  grower  should  not  wait  until  the 

Howard.)  f  , 

foliage  is  blackened  by  the  in- 
sects before  fumigating  the  second  time.  It  would  be  far  more  eco- 
nomical to  fumigate  regularly  once  in  two  years,  and  prevent  all 
blackening  of  the  foliage,  than  to  fumigate  once  and  wait  until  the  fly 


«See  discussion  of  this  subject,  pp.  9-14. 


60  FUMIGATION    FOR    THE    CITBUS    WHITE   FLY. 

had   increased  sufficiently  to    cause  blackening   of   the  foliage  and 

fruit  before  repeating  the  treatment. 

The  extent  of  the  damage  due  to  the  white  fiy  is  difficult  to  estimate. 
After  supplementing  his  personal  observation  with  direct  information 
and  estimates  on  this  point  from  more  than  50  orange  growers  who 
have  had  experience  with  the  pest,  the  author  would  consider  50  per 
cent  a  conservative  estimate  of  the  average  annual  loss  in  white-fly- 
infested  groves. 

The  consensus  of  opinion  of  the  orange  growers  referred  to  is  to 
the  effect  that  the  reduction  in  the  size  of  the  crop  alone  amounts  to 
50  per  cent  or  more,  leaving  out  of  consideration  the  loss  through  the 
checking  of  the  growth  of  trees,  the  retardation  of  ripening,  the 
expense  of  washing  the  fruit,  and  the  impairment  of  its  shipping 
quality  and  flavor.  In  many  cases  the  damage  from  the  fly  renders 
citrus  fruit  growing  unprofitable,  although  such  losses  are  usually 
unnecessary  if  proper  care  be  given  to  cultivation  and  fertilization. 
The  beneficial  effect  of  the  fungous  diseases  of  the  white  fly  and  the 
economy  of  fumigation  where  the  diseases  are  prevalent  will  be 
discussed  under  another  heading.  The  data  at  hand  concerning  the 
cost  of  fumigation  indicate  that  in  most  cases  the  expense  would  be 
sustained  by  the  increase  in  production  if  the  losses  of  the  white  fly 
were  only  10  per  cent,  instead  of  the  50  or  more  as  generally  estimated. 

Losses  from  scale  insects. — In  calculating  the  benefits  derived  from 
fumigation,  the  effect  of  the  treatment  on  other  citrus  pests  is  an 
important  consideration.  Fortunately  the  high  average  of  humidity 
in  the  citrus-growing  sections  of  the  Gulf  States  results  in  the  partial 
control  of  scale-insect  pests  which  would  otherwise  make  direct 
remedial  measures  necessary  for  profitable  crops.  The  thoroughness* 
of  this  natural  control  varies  greatly  in  different  groves  according  to 
local  conditions.  Fruit  infested  with  the  purple  or  the  long  scale  is  far 
less  valuable,  as  a  rule,  than  is  clean  fruit.  If  such  fruit  is  cleaned 
before  packing,  the  cost  is  usually  from  10  to  15  cents  per  box.  In 
the  markets  scaly  fruit  in  rare  instances  brings  as  much  as  fruit  free 
from  scale,  but  ordinarily  it  brings  from  25  to  75  cents  less  per  box, 
even  after  being  cleaned  by  hand.  If  not  cleaned  it  may  fail  to  find 
a  market  at  any  price.  "When  handled  by  orange  buyers  and  sold 
upon  the  tree,  even  a  small  percentage  of  scaly  fruit  frequently 
results  in  a  considerable  loss  in  selling  value  of  the  entire  crop. 

Direct  information  has  been  obtained  from  many  orange  growers 
and  shippers  concerning  the  effect  of  scales  upon  the  value  of  fruit. 
The  damage  reported  ranges  from  none  at  all  to  26  per  cent  of  the 
total  value  of  the  crop.  Ordinarily  from  5  to  15  per  cent  of  the  crops 
of  oranges  and  grapefruit  are  sold  as  of  an  inferior  grade  owing  to 
infestation  by  the  long  and  purple  scales.  One  grower  in  Lee  County 
reported  that  last  season  (fruit  shipped  in  December,  1906)  he  suffered 
a  loss  of  SI, 500  on  a  crop  of  1,000  boxes  of  oranges  and  2,000  boxes  of 


LOSSES    I  U<  »M    SCAL1      INSEC'J  S    l»HJ  \  I  .\  I  l.h. 


''.I 


grapefruit.  All  of  the  grapefruit  and  300  boxes  of  the  oranges  wrere 
scraped  bj  hand  to  remove  the  scale.  This  operation  cos!  between  $275 
and  $300;  The  loss  to  the  selling  value  of  the  oranges  was  about  v 
and  of  the  grapefruit  about  $1,000.  Man}  Instances  have  come  to  the 
writer's  attention  of  losses  From  scale  amounting  to  5  per  cent  of  the  t<>t  ;d 
value  of  the  crop,  [n  addition  to  direct  losses  of  the  kind  noted  above, 
frequently  more  serious  losses  arc  suffered  as  a  result  of  the  complete 
destruction  of  branches  and  weakening  of  the  vitality  of  the  trees  l>\ 
the  heavj  incrustations  of  the  scales  upon  the  main  branches  or 
trunks.  The  total  damage  from  scales  in  Florida  is  usually  too 
small  to  make  direct  remedial  measures  profitable,  but  when  this 
damage  can  be  to  a  Large  extent  obviated  at  the  same  time  with  that 
(A'  the  \\  liite  fly,  the  mat- 
ter demands  careful  con- 
sideration. It  is  the 
writer's  conviction  that 
in  the  cases  of  the  ma- 
jority of  groves  the  de- 
struction of  the  purple, 
long,  Florida  red,  and 
other  scale  insects  would 
represent  an  increase 
in  profit  which  would 
by  itself  offset  the  cost 
of  fumigation,  leaving 
as  clear  gain  the  ben- 
efits derived  from  redu- 
cing the  numbers  of  the 
white  fly  to  a  negligible 
quantity. 

The  Florida  red  scale 
{CJirysompliulus  ficus  Ashm.)  (fig.  10)  is  destroyed  with  a  thorough- 
ness near  to  absolute  extermination  by  the  same  dosage  which  is 
required  for  the  white  fly.  This  has  been  conclusively  proved  by  the 
experimental  work  conducted  by  the  writer  and  Mr.  W.  W.  Yothers 
in  January  of  the  present  year.  Not  infrequently  in  Florida  the  scale 
insect  referred  to  causes  sufficient  injury  to  make  fumigation  a  very 
profitable  procedure  against  this  insect  alone,  leaving  out  of  consid- 
eration the  effect  upon  the  other  pests  present. 

The  purple  scale  (Lepidosaphes  heckii  Newm.)  (fig.  11)  sometimes 
called  the  "brown,"  "oyster-shell,"  or  "hard"  scale,  is  of  greater  eco- 
nomic importance  than  the  Florida  red  scale  on  account  of  its  more 
wide-spread  distribution.  The  results  in  controlling  this  pest  accom- 
plished incidentally  to  work  against  the  white  fly  are  most  encouraging. 
In  the  same  grove  where  the  effect  of  fumigation  on  the  Florida  red 
scale  was  observed,  the  purple  scale  has  been  so  abundant  for  years 


Fig.  10.— Florida  red  scale  ( Chrysomphalus  ficus):  a,  Leaves 
covered  with  the  male  and  female  scales,  natural  size;  6,  newly 
hatched  insect  with  enlargements  of  antenna  and  leg;  c,d,  e,f, 
different  stages  in  the  development  of  the  female  insect,  drawn 
to  the  same  scale;  g,  adult  male  scale,  similarly  enlarged. 
(After  Marlatt.) 


62 


FUMIGATION    FOR    THE    CITRUS    WHITE    PLY. 


that  the  owners'  fruit-shipping  records  show  annual  Losses  from  this 
source  amounting  to  between  15  and  20  cents  per  tree.  Live  scales 
in  all  stages,  particularly  the  egg  and  adult,  were  very  abundant 
before  fumigating,  but  up  to  the  1st  of  June  careful  examinatioi 
thousands  of  leaves,  twigs,  and  green  fruits  by  Mr.  Yothers  and  the 
writer  have  not  led  to  the  finding  of  a  single  living  specimen  of  this 
species  in  the  section  of  the  grove  which  was  the  most  heavily 
infested.  At  this  season  of  the  year  there  is  usually  no  difficulty  in 
finding  more  or  less  abundant  specimens  of  the  spring  brood  of  this 
insect  even  where  it  was  so  scarce  the  previous  season  as  to  occasion 
no  appreciable  damage  to  the  crop. 

COST    OF    FUMIGATION    COMPARED    WITH    SPRAYING. 

In  Florida  the  average  cost  of  spraying  is  between  2\  and  :;  cents 
per  gallon  of  spray  applied.     When  spraying  is  done  with  such  effi- 


Fig.  11.— Purple  scale  (Lepidosaphes  beckii),  showing  different  stages  of  female:  o,  Newly  hatched  larva; 
b,  same  with  first  waxy  secretion;  c  to/,  different  stages  of  growth:  g.  mature  stale;  h,  same  inverted, 
showing  eggs;  i  and  ;',  half-grown  and  full-grown  female  insects  removed  from  scale.  All  much  enlarged 
(after  Marlatt). 

ciency  that  blackening  of  the  foliage  and  fruit  by  the  sooty  mold  is  pre- 
vented, at  least  three  applications  per  year,  and  usually  four  or  more, 
are  necessary.  The  mechanical  difficulties  of  spraying  with  as  much 
effectiveness  as  this  are  so  great  as  to  make  the  results  with  ordinary 
practices  far  inferior  to  those  from  fumigating.  In  fact  the  results 
with  sprays  have  with  few  exceptions  been,  unsatisfactory  in  con- 
trolling the  white  fly  or  preventing  the  blackening  of  the  fruit  and 
foliage.  In  many  cases  this  is  largely  a  result  of  the  character  of  the 
labor  which  it  is  necessary  to  employ  for  such  work.  For  the  pur- 
poses of  comparing  spraying  with  fumigating  in  regard  to  cost,  it  may 
be  considered  that  three  applications  of  sprays  per  year  will  control 
the  white  fly  in  a  satisfactory  manner,  although  in  actual  practice 
this  is  rarely  accomplished  unless  drought  or  fungous  diseases  offer 
material  aid 


FUMIGATION    v  '  ,;>l  B   BPH  kl  I  NO.  68 

'The  tented  tree  shown  in  Plate  VI,  figure 2,  measured  12  feet  over 
the  top  from  ground  to  ground  and  59  feet  in  circumference. 
According  to  the  table  given  in  the  appendix  a  tree  of  this  ize 
should  be  given  26  ounces  of  potassium  cyanid.  En  covering  a  tree 
of  this  size  ordinary  changing  poles  could  l>e  used  instead  of  the  up- 
right shown  in  the  illustration.  The  entire  cost  of  fumigating  the 
i  ree  for  the  \\  hite  fly  is  estimated  al  50  cents.  This  includes  36  cents 
cost  o\'  potassium  cyanid,  3  cents  cost  of  acid,  6  cents  cost  of  labor, 
and  .")  cents  cost  of  wear  and  tear  on  t  he  tent .  The  t  ree  shown  at  t  be 
[eft  of  the  tent  in  Plate  VI,  figure  2,  measured  A  1  feet  over  the  top  and 
53  feet  in  circumference.  According  to  the  tables  the  tree  requires  2b\ 
ounce-  of  potassium  cyanid.  the  cost  of  fumigating  therefore  being 
practically  the  same  as  for  the  fust  tree  mentioned.  Each  of  these 
trees  if  sprayed  would  require  six  or  seven  gallons  of  liquid  at  each 
application.  Three  applications  in  a  year  at  the  usual  cost  would  be 
from  45  to  <;:')  cents  as  compared  with  50  cents  for  fumigating.  The 
tree  shown  in  Plate  I  measured,  when  tented,  33  feet  over  the  top  and 
38fee1  in  circumference.  Atree  of  this  size  requires  12  ounces  of  pot  as- 
sium  cyanid  for  effective  fumigation.  The  total  cost  of  one  fumiga- 
tion would  be  about  27  cents,  including  16  cents  as  cost  of  potassium 
cyanid.  (>  cents  as  cost  for  Labor,  1  cent  as  cost  for  acid,  and  4  cents  for 
wear  and  tear  on  the  fumigating  tent.  A  tree  of  this  size  would 
require  at  least  3  gallons  of  spray  at  each  application,  and  during  the 
year  the  cost  for  three  applications  would  be  from  22  to  27  cents. 

These  data  on  the  comparative  cost  of  the  two  methods  of  control 
show  that  the  advantage  of  fumigation  over  spraying  for  the  first  year 
is  a  matter  of  greater  efficiency,  except  when  more  than  three  applica- 
tions of  spray  are  made,  when  fumigation  is  also  less  expensive. 
Fumigation,  however,  in  an  isolated  grove  or  under  favorable  condi- 
tions as  to  location,  when  properly  conducted  would  not  require  repeti- 
tion for  twoor  more  years.  The  best  of  spraying  could  not, unless  aided 
by  abnormal  climatic  conditions,  so  reduce  the  white  fly  that  the  num- 
ber of  applications  conld  be  lessened  the  second  year  without  interfer- 
ing with  the  degree  of  success  attainable  by  the  practice.  In  two  years 
the  cost  of  spraying  the  trees  above  referred  to  would  double  the  cost 
of  one  fumigation.  In  a  series  of  five  or  more  years  spraying  would 
doubtless  cost  fully  three  times  as  much  as  would  control  by  fumiga- 
tion, the  labor  involved  would  be  far  greater,  and  the  results  far  less 
satisfactory. 

FUMIGATION  VERSUS  NATURAL  CONTROL. 

The  present  investigation  of  the  white  fly  by  the  writer  and  his 
associates  covers  all  phases  of  the  subject.  Due  consideration  is  given 
to  all  possible  sources  which  give  basis  for  the  hope  of  effecting  eco- 
nomical control.  The  exposed  condition  of  the  pest  under  considera- 
tion, its  vulnerability  to  attack  by  natural  enemies,  the  high  deirree 
of  humidity  in  the  citrus-growing  regions  of  the  Gulf  States  which 
49918— Bull.  76—08—5 


04  FUMIGATION     FOB     THE    CITRUS    WHITE    FLY. 

favors  the  effectiveness  of  fungous  and  bacterial  diseases,  all  give 
basis  for  the  hope  that  complete  control  by  natural  enemies  will  be 
the  eventual  conclusion  of  the  white-fly  problem.  A  thoroughly 
scientific  and  practical  investigation,  however,  can  not  lead  to  lasting 
benefits  if  the  conclusions  represent  merely  desired  results  and  are 
unsupported  by  sufficient  evidence  and  experience.  While  a  great 
deal  has  been  learned  concerning  the  fungous  diseases  of  the  white 
fly,  the  present  investigations  of  this  Bureau  have  not  thus  far  shown 
that  any  method  can  be  relied  upon  to  materially  assist  nature  in 
controlling  the  pest  to  the  point  of  preventing  all  or  nearly  all  of  its 
injury.  The  dissemination  of  these  diseases  is  readily  accomplished 
under  certain  favorable  conditions,  but  how  far  artificial  dissemina- 
tion, at  its  best,  with  our  present  methods  goes  toward  the  successful 
control  of  the  white  fly  is  still  problematical. 

Manatee  County  is  the  only  large  orange-growing  district  where  the 
fungous  diseases  have  proved  of  much  assistance.  Data  obtained 
from  many  orange  growers  and  personal  observation  by  the  writer 
and  other  entomologists  connected  with  the  Bureau  of  Ento- 
mology indicate  that  the  fungi,  without  artifical  aid,  reduce  the 
injury  from  the  white  fly  about  one-third.  Undoubtedly  without  the 
aid  of  these  fungous  friends  the  damage  in  Manatee  County  would 
average  more  than  50  per  cent.  With  this  as  a  minimum  estimate, 
the  average  damage  in  Manatee  County,  allowing  a  benefit  of  one- 
third  from  the  fungi,  amounts  to  34  per  cent.  One  year  in  three,  it  is 
the  experience  of  the  growers  in  this  county,  the  fungi  have  so 
thoroughly  cleaned  up  the  pest  that  the  fruit  is  clean  and  requires  no 
washing.  The  following  year  the  insects  are  in  the  ascendency  and 
the  fruit  and  foliage  become  blackened  with  sooty  mold  to  as  great 
an  extent  as  can  be  observed  anywhere  in  the  State.  This  is  due  to  the 
fact  that  the  fungi  have  diminished  the  white  flies  the  previous  year  to  a 
point  where  they  cease  to  flourish.  Late  in  the  second  year,  however, 
with  the  fly  abundant ,  the  fungous  enemies  develop  rapidly.  The  third 
year  the  effect  of  the  blackening  of  the  foliage  is  apparent  in  a  greatly 
reduced  crop,  while  during  this  year  the  fly  is  again  reduced  to  a  negligi- 
ble quantity,  permitting  a  good  crop  of  fruit  to  set  and  remain  clean 
from  sooty  mold  during  the  following  season.  The  above  is  the  usual 
course  followed  in  individual  groves.  Considering  the  county  as  a 
whole  in  1906,  fully  three-fourths  of  the  groves  were  so  free  from  sooty 
mold  as  to  require  no  washing  of  the  fruit.  It  was  generally  con- 
sidered that  this  condition  had  never  before  been  equaled  since  the 
white  fly  first  obtained  a  foothold  in  this  county.  In  one  case,  how- 
ever, it  was  claimed  by  one  of  the  leading  orange  growers  that  an 
isolated  grove  had  become  practically  clean  through  some  unknown 
agency,  the  prevailing  fungous  diseases  not  being  present  in  sufficient 
abundance  to  accomplish  any  noticeable  result.  Nevertheless,  the 
fungous  enemies  referred  to  were  undoubtedly  of  prime    importance 


I  i    \m,  \  i  [ON    \  i  R81  -    \  \  i  i  i:  \i  >L. 

in  producing  e  of  freedom  from  \\lui<-  il\    damage  at- 

tained in    L906.     Other  conditions  may  have  had   minor  influence. 
A>  a  natural  consequence  of  the  lack  of  abundant  food  for  tin'  fun 
parasites  in   1906,  the  situation  in   1907  showed  a  complete  reversal, 
with  more  than  three-fourths  of  the  groves  thoroughly   blackened  by 
Booty  mold.     It  is  not  uncommon  to  find  that  individual  \-,w\ 

considerably  from  the  average  condition  of  the  groves  in  the  county 
as  a  whole. 

In  the  close  viciniix  of  Fori  Myers,  in  Lee  <  ounty,  the  fungi  have 
reduced  the  numbers  of  the  white  fly  to  a  greater  extent  than  observed 
at  any  other  place.  The  result  of  this  is  to  cause  a  considerable 
variation  from  the  usual  succession  of  predominance  of  host  and 
parasite,  but  in  the  course  of  a  ten-year  period  the  benefits  from  the 
fungous  diseases  under  natural  conditions  will  evidently  be  little  if 
any  greater  than  in  Manatee  County.  Tn  the  town  of  Fort  Myers  the 
conditions  are  not  comparable  with  those  in  large  commercial  groves. 
In  one  such  grove,  however,  located  on  the  south  side  of  the  Caloosa- 
hatchie  River,  nearly  opposite  Fort  Myers,  the  fungous  diseases  have 
proved  more  than  ordinarily  beneficial  during  the  past  two  years. 
There  is  strong  evidence  even  here  that  the  white  fly  will  regain  its 
usual  abundance  in  the  course  of  the  present  season  unless  artificial 
methods  of  control  are  resorted  to  or  experiments  result  in  the  dis- 
covery of  a  more  satisfactory  method  than  is  now  known  of  artifi- 
cially encouraging  the  growth  and  spread  of  the  fungous  enemii 

The  writer's  observations  lead  to  the  conclusion  that  in  99  per  cent 
of  the  groves  in  those  localities  where  the  fungous  diseases  are  most 
effective,  for  every  dollar  expended  for  well-conducted  fumigation  the 
profits  from  the  groves  will  he  increased  not  less  than  S4,  or  at  the 
rate  of  250  per  cent  on  the  investment.  If  the  expense  of  fumi- 
gation were  doubled  the  adoption  of  this  practice  would  still  be 
profitable,  at  least  until  such  time  as  the  natural  enemies  at  hand  can 
be  made  more  successful  or  new  ones  discovered  to  accomplish 
effective  control. 

The  spores  and  mycelium  of  the  fungi  are  not  affected  by  fumiga- 
tion, as  far  as  has  been  determined  thus  far.  In  experiments  in  the 
artificial  dissemination  of  the  brown  and  red  fungous  parasites  the 
results  obtained  were  as  satisfactory  when  the  material  was  collected 
from  fumigated  trees  as  when  collected  from  those  not  fumigated. 
Ordinarily  this  point  is  of  little  importance,  since  successful  fumigation 
would  always  result  in  practically  absolutely  checking  the  fun  her  multi- 
plication of  the  parasites  through  the  destruction  of  the  host  insects. 
The  further  multiplication  of  the  fungous  parasites  following  fumi- 
gation is  therefore  an  indication  of  ineffectiveness  of  the  treatment 
or  of  the  increase  in  the  numbers  of  the  pest  through  migration  from 
untreated  groves. 


APPENDIX. 
TABLE   OF  DOSAGE    FOR   THE   CITRUS  WHITE   FLY. 

The  table  of  dosage  herein  given  is  based  upon  the  author's  experi- 
ments conducted  in  January  and  February,  1907.  The  mathe- 
matical calculations  are  tabulated  and  explained  in  the  body  of  this 
bulletin.  The  most  important  object  of  fumigation  experiments 
against  the  white  fly  has  been  the  development  of  methods  for  the 
practical  utilization  of  the  fumigation  process  in  Florida  and  the 
gaining  of  a  knowledge  concerning  the  dosage  requirements.  The 
former  subject  has  already  been  disposed  of  through  the  methods 
herein  described.  The  investigations  concerning  the  latter  subject 
have  resulted  in  placing  fumigation  for  the  white  fly  on  a  basis 
whereby  the  process  may  be  used  against  tins  insect  with  greater 
economy,  thoroughness,  and  certainty  of  results  than  at  present  it 
can  be  used  against  any  other  species.  Incidentally  it  should  be 
remarked  that  the  dosage  requirements  for  the  white  fly  are  greater 
than  for  the  Florida  red  scale  and  perhaps  greater  also  than  for 
the  purple  scale.  It  is  beyond  the  scope  of  these  investigations  to 
determine  the  possibility  of  reducing  the  dosage  below  the  white  fly 
standard  without  interfering  with  its  efficiency  against  these  other 
pests.  It  is  sufficient  to  know  in  most  cases  that  the  white  fly  dosage 
is  equal  to  the  actual  requirements  for  the  pests  of  secondary  impor- 
tance. The  dosage  table  here  presented  does  not  necessarily  repre- 
sent the  exact  amounts  for  greatest  utility  in  the  case  of  the  different 
sizes  of  trees.  The  extensive  tests  of  the  dosage  table  during  the 
past  winter,  when,  as  has  been  stated,  nearly  4,000  trees  were  fumi- 
gated under  the  direction  of  the  agents  of  the  Bureau  of  Entomology, 
show  the  doses  recommended  to  be  very  close  to  the  necessary 
amounts  with  tents  of  equal  tightness  with  those  used  in  the  original 
experiments.  The  dosage  should  never  be  decreased  when  effective 
work  against  the  white  fly  is  desired,  but  under  certain  conditions  it 
may  be  increased  from  10  to  25  per  cent  with  advantage. 

If  there  is  a  slight  breeze  of  sufficient  strength  to  make  the  advisa- 
bility of  fumigating  questionable,  an  increase  in  dosage  of  10  per 
cent  or  more  may  allow  the  work  to  proceed  without  interfering  with 
the  efficiency ;  but  with  ordinary  tents  of  8-ounce  duck  such  increases 
do  not  offset  the  effects  of  strong  or  gusty  breezes,  which  sway  the 
66 


DOS  USE     I   M-.l.l  . 


••■7 


Bides  of  the  tent.  It  I  be  onl}  available  tents  are  of  inferior  quality  ;ui<l 
fall  short  of  being  as  nearly  gas-tight  as  the  best  of  material,  incre 
in  dosage  maj  be  advisable.  When  it  is  desired  to  fumigate  with  a 
thoroughness  approaching  extermination,  an  increase  maj  be  made 
of  from  LO  to  25  per  cent.  Such  a  course  is  frequently  advisable  to 
check  the  further  spread  of  the  fly  in  newly  infested  localities  or  in 
ne\\l\  infested  groves.  In  the  fumigation  of  very  small  trees,  20  feet 
over  or  less,  there  seem  to  be  certain  factors  sometimes  interfering 
with  efficiency  which  have  not  so  far  been  thoroughly  investigated. 
It  is  possible  that  in  the  using  of  crocks  of  2  or  3  gallons  capacity  \'<>v 
doses  Less  than  5  ounces  the  mixture  of  acid  and  water  fails  to  gen- 
erate sufficient  heat  to  cause  quick  chemical  action,  the  heat  absorbed 
by  the  jar  being  the  disturbing  factor.  This  may  be  partly  obviated 
by  using  powder  or  very  small  lumps  of  potassium  cyanid  when  the 
dose  is  5  ounces  or  less,  but  it  seems  advisable  also  to  increase  the 
amount  by  one-half  or  three-fourths  above  the  recommended  dose. 
If  the  size  of  the  crock  and  consequent  undue  loss  of  heat  is  the  prin- 
cipal disturbing  factor,  future  experience  may  show  that  it  is  desirable 
to  have  on  hand  for  use  in  fumigating  very  small  trees  a  supply  of 
half-gallon  crocks  or  1-quart  stone  chinaware  pitchers. 

In  the  table  the  amount  in  each  case  represents  the  next  half  ounce 
above  the  dosage  which  the  detailed  estimate  calls  for,  whenever  this 
dosage  was  more  than  one-tenth  ounce  above  the  even  ounce  or  half 
ounce.  For  example,  when  the  detailed  calculation  calls  for  19.2 
ounces  the  number  in  the  working  table  is  19^  ounces,  and  when  for 
19.7  ounces  the  number  is  20  ounces.  In  using  the  table  in  the  field, 
when  the  reading  on  the  graduated  tent  shows  the  approximate  dis- 
tance over  the  top  to  be  an  odd  number  of  feet,  the  next  even  num- 
ber above  should  be  selected.  In  the  same  way,  when  the  exact  cir- 
cumference is  not  shown  at  the  top  of  the  table,  the  next  highest 
number  should  be  selected. 

To  illustrate  the  method  of  using  the  table  of  dosage,  the  following 
examples  show  the  measurements  and  dosage  called  for  in  the  case 
of  five  trees  of  various  sizes : 


Measurements  of,  and  dosage  for  each  of  five  trees  of  various  sizes. 


Distance 
over  tented 

Circumfer- 
ence of 

Amount  of 
potassium 

cyanid 
called  for. 

tree. 

tented  tree. 

Feet. 

Feet. 

Ounces. 

28 

45 

10 

48 

60 

34 

54 

68 

47 

60 

74 

61 

72 

80 

89 

At  all  times  it  should  be  borne  in  mind  that  it  is  advisable  to  use 
one-half  or  even  1  ounce  more  than  called  for  by  the  table  rather  than 
the  smaller  amount. 


68 


FUMIGATION    FOR    THE    CITRUS    WHITE   FLY. 


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I  X  DEX. 


Ash.  prickly.      See  Xanthoxylum  clava-herculis.) 

Atmospheric  humidity  as  affecting  fumigation L2  I  I 

Banana  shrub.      See   \fagnolia  fuscatum.) 
See  Magnolia  i  irgirliana.  I 

Box  tents  or  covers  for  fumigating  small  trees  in  grove 54 

"Cactus,  prickly  pear.      Se<   Opuntia  sp.) 
('ape  jessamine.     (See  Gardenia  jasminoides.  I 

( !hemicals  for  fumigation,  cosl 

handling,  and  protection  from  moisture .- . . .         25 

proportion  of  water  and  acid 25  '27 

pnrit  y  required 25 

Cherry  laurel.      Sec  Prunus  laurocerasus.  I 

Chinaberry.      Sec  Melia  azedarach  and  M.  a.  wmbraculiformis.) 

wmphalus  ficus,  losses  prevented  by  fumigation 61 

Citrus,  food  plants  of  white  fly 10 

insect-,  history  of  fumigation 7-8 

trifoliata,  food  plant  of  white  fly 10 

white  fly.     (Set  White  fly.) 

( Joncerted  action  favoring  fumigation 9 

Conditions  favoring  or  necessary  to  good  results  in  fumigation 9-14 

Control,  natural,  of  white  fly,  versus  fumigation 

( Jost  of  fumigation  compared  with  spraying 62-63 

Cubic  contents  of  tented  tree,  methods  of  computation  in  fumigation 39-40 

Cyanid  oi  potash.     (See  Potassium  cyanid.) . 
Derricks.     (See  Uprights.  | 

Dews  as  affecting  fumigation '. 12   11 

Diagram  of  grove  as  guide  in  fumigation 23-24.  38 

Dimensions  of  tented  tree,  methods  of  computation 39  40 

Diospuros  Jcaki.  food  plant  of  white  fly 10 

virginiana,  food  plant  of  white  fly 10 

Dosage  requirements  in  fumigation  against  white  fly 40-50 

table  for  fumigation  against  white  fly ■ 

Economy  of  treatment  by  fumigation 59-63 

Equipment  for  fumigation 14-24.  51  i  58 

Expense  of  fumigation „ 

Ficus.     (See  Fig.) 

altissima,  food  plant  of  white  fly 10 

Fig,  reported  food  plant  of  white  fly 10 

Food  plants  of  white  fly 10 

Food  plants,  other  than  citrus,  of  white  fly.  absence  or  elimination  favoring 

control  by  fumigation 9-10 

Fumigating  tents.     (See  Tents.) 

69 


70  FUMIGATION   FOR   THE   CITRUS   WHITE   FLY. 

Page. 

Fumigation  against  citrus  insects,  history 7-8 

white  fly,  absence  or  elimination  of  food  plants  other  than 

citrus  favorable 9-10 

appearance  of  dead  larvae  and  pupae 50-51 

chemicals,  cost 58 

handling,  and  protection  from  mois- 
ture   25 

proportion  of  water  and  acid 25-27 

purity  required 25 

concerted  action  favorable 9 

conditions  favorable  or  necessary  to  good  results. .  9-14 

cost  compared  with  spraying 62-63 

density  of  gas  at  various  heights  above  ground . .  51 

dosage  requirements  with  bell  or  hoop  tent 49-50 

sheet  tent 40-49 

economy  of  treatment 59-63 

effect  on  trees  and  fruit 51-54 

equipment 14-24 

expense 56 

history 7-8 

isolation  of  grove  favorable 9 

losses  prevented  thereby 59-60 

measuring  trees 30-35 

meteorological  elements  favorable 11-13 

method  of  generating  gas 35-36 

handling  bell  tents 29 

sheet  tents 27-29 

methods  of  computing  cubic  contents  of  tented 

tree 39^0 

dimensions  of  tented  trees  39-40 

miscellaneous  experiments  and  observations 50-54 

requirements 22-24 

nursery  stock  for  shipment 54-55 

poles  for  handling  tents 20-21 

precautions 55-56 

procedure 27-38 

proportion  of  water  and  acid 25-27 

season  of  year  favorable 10-11 

table  of  dosage 66-68 

tents,  care 19-20 

construction 15-19 

mildew-proofing,  oiling,  and  painting 19-20 

shrinkage 17-18 

styles 14-15 

time  required 38-39 

trees,  regularity  of  setting  favorable 14 

size  favorable 14 

small,  in  the  grove 54 

nursery 54 

uprights  for  handling  tents 21 

versus  natural  control 63-65 

work  routine 36-38 

Fungous  diseases  in  control  of  white  fly 64-65 


INDEX.  VI 

Gardenia jattninoides,  |'<><»<I  planl  of  white  fly 10 

lensit)  at  various  heights  above  the  ground 

method  of  generating 

Qrapefruit  as  affected  by  fumigation 

trees  as  affected  by  fumigation 

Grove,  diagram,  as  guide  in  fumigation 

Humidity  as  affecting  fumigation 12-  I  I 

Hydrocyanic-acid  gas.     (Set  Fumigation 

leerya  purchasi,  control  by  fumigation 7 

[eolation  of  grove  favoring  fumigation 

Jessamine,  cape.    (See  Gardenia  jasminoides.) 

"Jingler" Lfi 

Labor  for  fumigation,  cost 

Laurel,  cherry.    (See  Prunus  laurecerasut.) 

L,  pido&apfo  8  b<  chit,  losses  prevented  by  fumigation (i  I  -62 

Light  as  affecting  fumigation  against  white  fly 11 

TAgustrum  spp.,  food  plants  of  white  fly 10 

Lilac  food  plant  of  white  fly 10 

Losses  from  scale  insects  prevented  by  fumigation I 

white  fly  prevented  by  fumigation 59-60 

Magnolia  fuscatum,  food  plant  of  white  fly 10 

virginiana,  food  plant  of  white  fly 10 

Measurements  of  trees,  necessity  in  fumigation 30-31 

Melia  azedarach  and  M.  a.  umbraculiformis,  food  plants  of  white  fly 10 

Meteorological  elements  favoring  fumigation 11-13 

Moisture.     (See  Humidity.) 

Mold,  sooty,  resulting  from  white-fly  attack 64 

Nerium  oleander,  food  plant  of  white  fly 10 

Nursery  stock  for  shipment,  fumigation  against  white  fly 54-55 

trees,  fumigation  against  white  fly 54 

Oak,  water.     (See  Quercus  nigra.) 
Oleander.     (See  Nerium  oleander.) 

Opuntia  spv,  use  of  juice  for  painting  fumigating  tents 19 

Orange  fruit  as  affected  by  fumigation 53-54 

trees  as  affected  by  fumigation 51-53 

Palmetto,  scrub.     (See  Sabal  megacarpa.) 

Pear,  food  plant  of  white  fly 10 

Persimmon,  Japan.     (See  Diospyros  kaki.) 

wild.     (See  Diospyros  virginiana.) 

Poles  for  handling  fumigating  tents 20-21 

Potassium  cyanid  for  fumigation,  cost 58 

handling,  and  protection  from  moisture 25 

purity  required 25 

Prickly  ash.     (See  Xanthoxylum  clava-herculis.) 

pear  cactus.     (See  Opuntia  sp.) 
Privets.     (See  Ligustrum  spp.) 

Pruning  trees  as  aid  in  fumigation 14 

Prunus  caroliniana,  food  plant  of  white  fly 10 

laurocerasus,  food  plant  of  white  fly 10 

Pyrus  sp.     (See  Pear.) 

Quercus  nigra,  reported  food  plant  of  white  fly 10 

Sabal  megacarpa,  food  plant  of  white  fly 10 


72  FUMIGATION    FOR    THE    CITRUS   WHITE   FLY. 

Tage. 

Scale,  black,  control  by  himigatioD 7 

"brown."      See  Lepidosaphes  bed 
cottony  cushion.     |  See  Icerya  purchat 
Florida  red.     (See  Chrysompfialus  jicus.) 
"  hard."     (See  Lepidosaphes  beclcii.) 

insects,  losses  prevented  by  fumigation 60-62 

••oyster-shell."     (See  Lepidosaphes  beckii.  i 
purple.     (See  also  Lepidosaphes  bechii. 

control  by  fumigati<  m 7 

red,  control  by  fumigation 7 

Seas >n  of  year  favoring  fumigation 10-11 

Shedding  of  foliage  in  fumigation 52-53 

Shrinkage  of  tents 17-18,  32 

Spraying,  cost  compared  with  fumigation 62-03 

Sulphuric  acid  for  fumigation,  cost 58 

handling,  and  protection  from  moisture 25 

purity  required .' 25 

Sweet  bay.     (See  Magnolia  virginiana.) 
Syringa  sp.     (See  Lilac.) 

Table  of  dosage  for  fumigation 66-68 

Tangerine  fruit  as  affected  by  fumigation 54 

trees  as  affected  by  fumigation 52 

Tannin,  use  in  mildew-proofing  fumigating  tents 19-20 

Tents,  bell,  construction 15 

dosage  requirements 49-50 

method  of  handling 29 

box,  construction 15 

dosage  requirements 54 

care 19-20 

construction 15-19 

cost 56-57 

hoop.     (See  Tents,  bell.) 

marking  for  estimating  dosage 31-35 

mildew-proofing,  oiling,  and  painting 19-20 

sheet,  dosage  requirements 40-49 

method  of  handling 27-29 

shrinkage 17-18,  32 

styles 14-15 

Time  required  in  fumigation  of  grove 38-39 

Tray,  commissary,  for  fumigation 22 

Trees  as  affected  by  fumigation 51-54 

measurements  in  fumigation 30-35 

regularity  of  setting  favorable  for  fumigation 14 

size  when  tented,  methods  of  computation 39-40 

sizes  most  favorable  for  fumigation 14 

small,  in  grove,  fumigation  against  white  fly 54 

nursery,  fumigation  against  white  fly 54 

Uprights  for  handling  fumigating  tents 20-21 

Viburnum  nudum,  food  plant  of  white  fly 10 

"White  fly,  appearance  of  larvae  and  pupae  when  destroyed  by  fumigation 50-51 

citrus.     (See  White  fly.) 

control  by  fumigation,  history 7-S 

food  plants 10 


I X I )  K  X 


White  il\  fumigation,  absence  or  elimination  of  food  plant*  other  than  i  iti 

favorable  9-10 

appearance  of  dead  Ian  as  and  pupae  0  51 

chemical  

handling,  and  protect  ion  from  moisl  ure 

proportion  of  water  and  acid 

purity  required  25 

con. cried  action  favorable 

conditions  favorable  or  necessary  to  good  results 9  II 

density  of  gas  at  various  heights  above  ground 51 

ige  requirements  with  bell  or  hoop  tent 19 

sheet  tent 10    19 

economy  of  treatmenl 5 

effect  "ii  trees  and  fruit 5]  54 

equipment ' 14-24 

expense •"" 

isolation  of  grove  favorable 9 

losses  prevented  I  hereby 59 

measuring  trees 30 

meteorological  elements  favorable 11-13 

method  of  generating  the  gas 0 

handling  bell  tents lm» 

sheet  tents 27-29 

methods  of  computing  cubic  contents  of  tented  tree...  39 

dimensions  of  tented  tree 

miscellaneous  experiments  and  observations 50-54 

requirements 22-24 

nursery  stock  for  shipment 54-55 

poles  for  handling  tents 20-21 

precautions 55-56 

procedure 27-38 

season  of  year  favorable 10-11 

table  of  dosage 66-68 

tents,  care 1 9-20 

construction 15-19 

milaew-proofing,  oiling,  and  painting 

shrinkage 17-18 

styles 14-15 

trees,  regularity  of  setting  favorable 14 

size  favorable 14 

small,  in  grove 54 

nursery . 54 

uprights  for  handling  tents 21 

versus  natural  control 6 

work  routine 36-38 

Wind  as  affecting  fumigation 12 

Xanthoxylum  elava-herculis,  food  plant  of  white  fly 10 

o 


UNIVERSITY  OF  FLORIDA 


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